I would like to make an aggressive repertoire with the move 1.Nf3 but I'm not sure what to do about 1...c5. My first thought was to simply play the open sicilian. That's aggressive enough but there are move order issues.

For example after 1.Nf3 Nf6 since I have no intention to play against the entire mess of 1.d4 defences, 2.c4 is the only move. But the problem now is that Black has 2...c5 which is a symmetrical English. I don't see the point in playing 1.Nf3 c5 2.e4 if Black has this option.

But now another problem arises. After 3.Nc3 (3.d4 cd 4.Nxd4 e5 5.Nb5 d5 6.cd Bc5 is messy. I play it with Black and don't want to with White.) Nc6 4.d4 cd 5.Nxd4 g6 and now I have to play a Maroczy bind. Now the Maroczy bind is White's best chance for advantage but in my games the only time Black plays ...c5 is to get into a Maroczy bind. I don't care how good it is - I don't want to play it over and over and over again... The good thing about 4.d4 is that the position opens up but if Black is going to only play that one line then I won't enjoy playing it.

White is not forced into playing d4 but those lines of the symmetrical English are just way too complicated. At least with d4 the game opens up and I have better chances but without d4 I end up moving my pieces in circles until someone blunders a pawn...

So I'm not really sure about what to do about this. I like 1.Nf3 becuase it cuts down A LOT of theory from 1.d4 and 1.c4 but the delayed ...c5 is a problem. It leads to positions that I either don't like or can't play.

I have managed to significantly decrease the number of positions that I have to play. The only 1.d4 line that I actually have to play is the queen's gambit exchange. The the nizmo and slav are both avoided with English sidelines. The KID is also handled by an English setup to keep theory low.

The QID is met with 1.Nf3 Nf6 2.c4 b6 3.Nc3 Bb7 4.d3 e6 5.e4. This is a really old variation that Petrosian used a few times so no one is going to know it anyway.

That only leaves 1...d5 which I meet with 2.c4 (2.d4 would compromise the entire repertoire) and now 2...e6 transposes to the queens gambit exchange and 2...c6 can be met with the anti-slav as usual. 2...dxc4 3.Na3 doesn't require me to memorize much and 2...d4 3.e4 is a reversed czech benoni that I already use with Black. There is no theory at all on 3.e4 and that's a plus.

Most of these lines won't give White the advantage but I can get by with ideas instead of having to know any theory.

OH, well.... lucky me i just switched back to e4...

I don't think there is a best first move - each move allows and disallows certain lines.  Pick something that works for you.