I went from iPhone 4 on Sprint, to canceling my plan and getting an unlocked HTC 8x (verizon model) and using it with T-mobile's prepaid.
I thought I would miss my iPhone but I honestly don't. I'm in love with the screen on the 8x and I'm a music junkie so Beats audio paired with my NOC NS400 Titanium in ears is a real treat.
Skype is still in beta but i get better quality making "computer to computer" (without video) phone calls than I did with my iphone. the camera takes stellar pictures (i've heard the lumia 920's is insane but the pictures I take upload to facebook, not a museum) and the front facing camera takes hi def video.
I've never been an app junkie so the sparsity on the windows store really doesn't bother me. I'm waiting for my bank to develop an app and instagram and if they do, well then I'll have pretty much everything i used on my iphone.
So far i've dropped my phone twice (no case) and it withstood the drops with grace. i have no build quality issues but recently it did reboot on me a couple times, which doesn't really bother me since it's a mini computer... and sometimes these smart phones need to be restarted.
hope this helps with your decision