Personally, I prefer ARM's move, because while it's a complexity increase now, it paves the way to someday drop support for 32-bit ARM, which would be a major architectural simplification. It also means that, as a programmer, when you're in 64-bit mode you aren't burdened by all of that weird backwards compatibility stuff going back decades—you get a relatively clean ISA.

(I do have some gripes with AArch64, to be fair: there are too many addressing modes and the condition codes are unnecessary. But I'll take anything that moves us in a more RISC-y direction.)