Default [Q] Will the HTC One (M8) Or GS5 Be Best To Get For Custom ROMs From T-Mobile?

I have the Xperia Z1s and am waiting to see if the Z2 comes to T-Mobile in the next couple of months, but as much as I like the Z1s, there isn't even root for it. So next week the S5 and HTC One will be released and I'd like to keep it until the Z2 is released of some sorts in the U.S. I've read that the S5 will have a locked bootloader on T-Mobile but nothing yet about the HTC One. Any thoughts?