Alekhine or Petrov defense?

Which should I pick up and learn? Which is more fun to play? Is one more sound than the other?

Petroff is definitely far more sound!  I have played it myself a few times despite my heavy preference for the French, but nothing wrong with it.

Alekhine is DUBIOUS AT BEST!

They're both fine... look at the basics of both, play a little bit of them and see which one you like better... you're not going to win or lose more or less because you played petroff or alekhine

petroff is more balanced and even, it has a fame for being "drawish", and a little easier to play because you have a bit more space whereas alekhine is a bit more tricky... but nothing that would make much difference in  online rapid blitz and bullet

I think you need to find your own playingstyle and ask yourself which one of them fit you the most. The two openings are VERY different in their characteristics. Ask yourself what you are looking for in a defensive system.

Are you okay with a draw as black? Is your main goal to equalise? Do you like to play positional and symmetrical positions? Then the petroff is better.

Do you want to fight for the win rather than to aim to equalise? Do you enjoy playing unbalanced and sharp positions? The Alekhine is the way to go.

I’ve been leaning to the latvian gambit as of late as a response to e4. I always run out of moves playing alekhine, its so much fun though. Guess i don’t fully like hypermodern openings. I feel as though alekhine is solid but lacks natural ideas to play it or i don’t know them.

I believe Alekhine only played 1... Nf6 because he usually got bad positions, and relied on his opponents to make an opening mistake.

They are both fine. In the non-master database of games over at that other website, the Alekhine wins 46% of games for black, while the Petrov wins 44% of games for black. It's not any kind of difference that you'll actually notice in play. It's not a bad opening at all. On the one hand you have ThrillerFan who is the site's #1 fan of the London System saying that it's dubious, and on the other you have GM Daniel Narodistsky who loves it and is rated #7 on the chesscom leaderboard in blitz and #1 in bullet. You decide whom to trust.

The thing about the Alekhine is that you don't play it like other openings. You can't just put your pieces out there and hope for the best; rather, you really have to learn it. There are five main variations that white plays against it, and you have to be prepared for those. Luckily, even really good white players usually know only about four or five moves of theory and then they are just making it up. Most think "I know the four pawns is good," push f4, and then they have exhausted what they know. Believe it or not, black wins 4% more often than white in the four pawns because going into mainline theory against an Alekhine player is usually a bad idea. The Alekhine player plays it every time they see e4 and white sees it maybe once every couple of hundred games. Who would you trust in that fight?

If you choose the Alekhine, learn the theory. If you don't want to bother with theory, pick the Petrov.

Soundness is a weird metric. I'm not even sure I know what it means. In non-master games, the Alekhine wins slightly more. In Master games, the Petrov is 29/59/12 (win/draw/loss) and the Alekhine is 37/37/26. You lose a lot more as Black, but you also win a lot more, and draws are far less common. If by "sound" you mean "less likely to lose", then yes, it's more sound. The Alekhine, however, gives far better winning chances.

And "fun" is definitely a subjective metric. Personally, I think the Alekhine is a ton of fun. You sit back, watch white expand, look for your spots, and then counterattack. I like that. What I don't like are slow, often symmetrical games that put me to sleep. For me, the Petrov is the worst possible opening I could choose.

Petrov is more sound, but the alekhine is much more interesting to play. I have over 2,200 games with 1...Nf6! and I score ~50% with black.

The only thing opening that scores more for me is the sicilian.

At worst, it's slightly better for white, and still within the drawing margin. Your opponents don't play like stockfish, neither do mine.

Of course this is a subjective statement. In both openings it is possible to get completely symmetrical structures.

The petrov gets really sharp after e4 e5 nf3 nf6 nxe5 d6 nf3 nxe4 nc3 nxc3 dxc3. This leads to opposite side castling, and attacking play by both  sides. There are very openings that are 100% "boring", and there are very few openings that can't lead positional play. Chess involves both positional chess and attacking chess, it is next to impossible to avoid one or the other.

True. Pretty much all openings have their boring and their sharp lines. 

I would never call your nimzowitch/modern a sharp variation. Sure, according to Andrew Martin, this variation was brought to life by players who were trying to spice up the Petrov. However, this "sharp" variation scores 62% draw and 27% for white. So if white is trying to sharpen the game up, he or she is not doing so successfully.

The starting position has an almost 100% draw rate in correspondence chess. At a high enough level every opening will either have a 100% score for white/black, or a 50% score. Master play has little effect on us plebs. Not only that, "sharp" does not equal decisive. Plenty of positional openings have low draw rates.

I think that the decisive result of an opening is one of the most critical factor to determine the openings "sharpness". Even for being master games, 62% is way higher than other openings. see below:

Examples of some more sharp defences to e4: Alekhine 37% draw, sicilian 42% draw, pirc 36% draw. 

Example of some more solid/positional defences to e4: Petrov 62% draw, Rubenstein french 52% draw, Caro kann main-line 50% draw.

For me, sharpness is determined by the amount of moves every turn that does not give the player a loosing position. Thus, usually leading to less drawn games, since the mistakes made tend to be critical mistakes.

That is relative to the time control and the players strength. Anyways, the open catalan is "sharp", but it still has a draw rate of 53%. I would rather trust the opinion of an IM than the opinion of a clubplayer. Plus, "sharpness" is arbitrary, the line that divides sharp and positional is open to interpretation.

Jeez. Just look at the numbers. In high level play the Petrov draws 59% of the time and the Alekhine just 37%. In non-high level play, draws are rare regardless of the opening, with just a 1% difference between the two, even in the highest non-titled category in rapid (2500 on Lichess). In the 2500 category, the Petrov and the Alekhine perform almost identically, and again in the 2200 category. In the 2000 category the Alekhine has about 5% on the Petrov, and in the 1800 category, Black wins 50% of games while white only wins 45% making the Alekhine the clear favorite.

If anyone doesn't trust me on these numbers, I'll make screen shots, but please don't make me. The point is, that from any metric other than "in theory" they are equally sound. In practice, at the intermediate level, you are more likely to do better with the Alekhine and for more advance players, you are ever so slightly more likely to do better with the Petrov, but it's only like a percentage point.

you can play any opening at this level, cuz its decided by final blunder. try both and see what fits you more, both openings perfectly sound for beginers. I personally like many  positions that arise from alekhine and use it against e4 all the time. I even play nc6 against d4 (Mikenas defense) which somewhat resembles alekhine from different side. now that is example of unsound opening, cuz it has some problematic lines for black, but most of the time it leads to two knights tango (Lithuanian opening) which is fantastic for black, massive kingside attacks and domination on dark squares. thats fun!

petrov is significantly better