There's a reason that the Nexus 4 has been sold out almost since it hit the Play Store: for custom ROM enthusiasts, buying anything else is a crapshoot. Assuming that the bootloader is unlocked (or can be,) you've just got to hope there's enough adoption among ROM developers to ensure a steady stream of builds. Owners of T-Mobile's former flagship, the HTC Amaze 4G, have had relatively good options in this area, and they just got a little better: the CyanogenMod team has released official nightly builds of CM10. Owners of the older Sensation 4G can also join the party.
Both devices are supported in an experimental capacity.