Look at ur budget go for xt720 la bro..no regret 

Both have its pros and cons..

for the wildfire
pros- cheap, compact, and uses sense UI, android 2.1 (i tink)
cons- poor screen resolution, and because of this, some apps might not be compatible

for the x10
pros- nice big screen, higher resolution, more apps should be supported as compared to wildfire, good camera (i would say the best camera of all currently available android fones)
cons- more expensive, android 1.6 only at the moment, timescape can be a little sluggish

so its up to u.. why dont u also check out the HTC legend. slightly faster processor as compared to the wildfire, also uses sense UI, better screen resolution, most apps supported, android 2.1 (sadly no 2.2 yet for this fone), and not very expensive (but more expensive than the wildfire tho)

you can also check out the motorola xt720, which is also a good fone, but if u plan on rooting and flashing to custom roms, if im not mistaken this fone does not allow that.. and the RAM on this fone is a little on the low side, but besides that, it is a good fone..

another fone would be the motorola milestone, good fone, but might as well wait for the milestone 2..

if ur budget can go higher, u can also check out the desire and the Samsung galaxy S..

overall, i would say tat if between wildfire and x10, i would personally go for the x10 coz i prefer larger screens, but do also take note of the HTC Legend