all games are not created equal

Biggest difference between these two games for me is how they define a combo.  In Tekken 5, a combo is a specific sequence of button presses.  There are times where you can link several of these predefined combos together, but at the base of the combo system are these predefined combos.

With SF4, you have moves that you can chain together in creative ways to create combos.  There is a lot of exact timing involved, but it feels a lot more open-ended as opposed to T5 where you are trying to make sure that once you get that first hit of a combo in that you can continue it.

Because of this, I really have to go with SF4.  The game looks great, plays great and can be a lot of fun to play.  Not being tied down to a combo system like T5 feels nice when you just wanna pick up a game and have a lot of fun, and still have the complexity of an awesome fighting game when you're ready for it.

Honestly, I just enjoy 3D fighters better than 2D.  I love SFIV very much, but I enjoy the more reasonable techniques used in Tekken 5 as opposed to the fireballs and insane hits used in Street Fighter. 

I'm terrible at Street Fighter.  I may very well be the worst SFIV player online.  I played over 20 matches last night and lost every single one of 'em, but the game is still fun.  The characters are well balanced and make for a lot of interesting matches.

Tekken 5 still remains largely unchanged from Tekken 3.  The characters are all well balanced once again, and it offers plenty of customization options for your fighter's appearance.  The open and closed arenas are all a joy to look at and play in, and feature some pretty sweet music to go along with 'em.

SFIV wins because it has a better overall lasting appeal.  The graphics are nice and crisp and look terrific, despite being confined to a 2D plane.  The characters facial expressions get joyfully disproportioned when they get attacked, and makes for some awesome freeze-frame screens when the final blow is landed.  Plus, SFIV keeps altering it's winning game mechanics ever so slightly, this time adding a revenge meter and focus attacks.

We'll have to wait and see if Tekken 6 can offer something we haven't seen before.