Myself, I would play 7...Be7. Neil McDonald's recent book provides good coverage.

I recommend that you play both 7...a6 and 7...Be7 because as far as I know, these are the two moves with the best theoretical reputation at present. In terms of model players, Morozevich is probably the best guide.

The best one ... because it is the best  
OK I know, it's lazy answer, but it's because question is inaccurate, and I am forced (as many readers) to guess, you mean: "in the "Boleslavsky line with f4 and Be3 for White".  No ?
White can play 1.e4 e6 2.d4 d5 3.Nf6 4.e5 Nfd7 5.Nce2!?, system played by Anand (can lead to French Tarrasch ) and not sure some  moves you proposed in title are useful.
You must replace 7...dxc with 7..cxd.
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All moves you gave are played in the Boleslavsky line and each one has specific purpose. One main plan for White is long castle (after Qd2) and an attack over the kingside castle, hence usually Black delays cxd4 till White engineers long castle, because closing with c5-c4 and starting attack with Bb4+Qa5 can lead to sharp attack for opposite castles. Another plan is early cxd4 to play Bc5 fighting for the a7-g1 diagonal and the d4 strong point control. Another plan is Qb6 for double-attack b2+d4 leading usually to native main lines of Boleslavsky with Na4 + c3. White can also use Be2 plan with short castle and quieter play...quieter because a d4 square blockade is more difficult to get (Nc3-Ne2-Nd4 impossible) and light square bishop is not well placed to counter f6 or f5.
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I usually replay to such post by "nobody can judge at current position. Propose one variation" or "which one do you like ?"..because you will choose one, only because you exactly know what are pros andcons for each one.

Hello,

I'm going to add the french Stenitzl to my openings. Which 7. move would you recommend and why?

thank you!

Rainer