i think it depends on the type of music you are doing, but the fact you are not using a computer does nudge it to the cirklon, IMHO
ive heard a lot of really good things about it, never used one myself - but supposedly the timing is rock solid, also its got multiple midi outputs (damn!) and that is the hotness if you have a bunch of outboard gear already
so that would be my first choice, but yeh id probably sell the evolver and tetra and get an A4 as well… and ive owned the desktop evolver and the monoevolver myself, and i know how awesome it is - but still, yeh i think the A4 would crush it in the same category of analog/sound design wildness with built-in sequencer/modulations