Nimzo Indian or Semi Slav for Repertoire Choice?

Which opening would be better for long term gain with both positional play and tactics?

(I am leaning towards the Semi-Slav)

The Botvinnik Variation in the semi-Slav gives lots of tactics and play for black though...

The Nimzo provides a clear strategy - double White's pawns on the c-file and then attack them. You get dynamic piece play (no trapped LSB as in the Semi-Slav) but often cede the centre to White - as Magnuts said, comes down to your style of play preferences

Lines like the Rubenstein in the nimzo for instance tend to lead to boring play (from firsthand experience). Is there a way I could spice up these lines?

One idea might also be to play the semi slav with a nimzo move order (against 3 Nf3)

The seni slav is a dynamic weapon- just see schandorff's book by quality chess

*semi

Either... both nimzo and semi slav are proven at WC level.

I'm not so sure about the "double white's pawns and attack them" stuff. The point of Bb4 as I understand it is to prevent white, at least at the time being, from playing e4, and then play in the centre with moves like c5 and d5. A lot of the time when the bishop on b4 has done its job it is retreated to e7 or d6.

There are a couple of problems with this plan of trying to induce doubled pawns. If black ever plays d5 then white plays cxd5 and now has a strong structure. If black doesn't play d5 the doubled pawns on the c-file actually control a lot of central squares and are hard to attack.

In the Hubner Variation black does take on c3, but it's not to give white doubled pawns, but rather to trade off the dark squared bishop and then set up a dark squared blockade.

I'm curious whether you actually have a source - is there a book where you read that in the Nimzo black attacks the doubled c-pawns, or do you have GM game examples of this strategy? Otherwise it really just seems to me to be a myth.

Yes, good point... the nimzo can be played many different ways.

As said above the doubled pawns are often regarded as a strength nowadays... but is still an option. One can retreat the bishop, but this is quite tricky also? Most experts focus on rapid development, with the bishop being disposable? 

Nimzo can be played aggressive or solid, which is why master player love so much?

Also, semi slav is not as super solid as one might think... can easily become a cramped mess at club level, as Lion has learned... semi tarrasch or classic slav might be a safer option?

Thanks for all your help guys! I have decided to play both, the semi Slav with a nimrod move order

*Nimzo

Also, I like crazy chess

Either of those two, or any other sound Black opening will be just fine. It hardly matters which opening you choose--so long as you learn it. Basically, the choice of which respectable opening to play is of almost no importance.

Good point

The Semi Slav moves are easier to learn (d5 c6 e6 Nbd7 Bd6 Nf6 OO), though they lead to a very complex middlegame I think

Can you think congrandalor?!

His wife leave him... because he could not satisfy... maybe she need a real Lion?!