Observations
Pathfinder (Beta) is indeed available for free download at the moment, I think. The downside of Pathfinder is that while the book is basically Paizo's version of the PH, they have no Monster Manaul, no DM Guide, or certainly none of the myriad Complete.... series available for 3.xx. This same thing appllies to 4E, but new 4E material is being released almost every month. So, at this rate, 4E will catch and possibly surpass 3.xx in a very few years.
I am familiar with both systems (and Pathfinder). I like both systems (and Pathfinder). I don't think that 4E stymies creativity, because the creativity does not come from the system, it comes from the player. I will say that, for now at least, 3.xx has a much broader supply of monsters available to the DM. But, realistically, even one Monster Manual has more material than even a Superhuman DM could possibly use in a year or two of play. (And we all aspire to be that Superhuman DM, I know...)
So, I leave you with the way that I have answered this question for myself: I STRADDLE THE FENCE AND PLAY BOTH 3.5 AND 4E AS MUCH AND AS OFTEN AS I CAN!
But, having said that, I realize that the expense of the books may be a limiting factor for very much of this sort of behavior. And, if that's the case, my suggestion is that you go to ebay, and bargain-hunt. Anyway, my advice is this -- pick a system, either system. Read it, learn it, play it, but don't actually LIVE it ('cause that's just sad and weird). Then, when the new wears off, switch to the other system. "Wizards" will love you.