Knowing what I know now, I'd buy neither of them.
I'd buy a HTC, sell it in half a year or so (at least wait untill you're sure that WP8 is worth it), and then go for a WP8. But that's what I would do, I prefer customization over WP. Even if a HTC won't be as smooth as WP on some fronts, I'd have a lot more fun with it then I do with this Lumia I have now, and heard only good things about HTC lately, and be honest, they are very good looking. WP is BORING as ****. About 4x per day it goes : tap tap, done. And that's it, apart from a quick game here and there. You just can't do a lot with it for now. Way too limited on all fronts. But again, that's just me apparently.
WP, I'd leave it alone for a while, trust me, you'll be dissapointed if you buy it now.
iPhone should be ok also, but then again I would wait for iPhone 5 instead of spending the money on it now.
cheers.