Sony phones have great hardware, build quality, and many are well supported. However, if you buy a sony phone with the intention of using any custom ROM, make sure to avoid buying a carrier-subsidized model due to the locked bootloader. There used to be a third party method of unlocking the bootloader, but Sony went out of their way to kill it. Sony only supports bootloader unlocking on unlocked, unbranded models - that means buying a carrier-subsidized handset and then entering a sim unlock code won't do anything for the bootloader.
of course, in most places this option is quite expensive, so if your budget only allows for a contract subsidized model then sony should be avoided.