[Obioban]

I'd go with evolve for a number of reasons:
a) I think they're a better tuner in general, both in customer service and ability to tune
b) They've been tuning 130i's since they came out, since they're based in europe. They know what to do to get power out of them on top of enabling DISA
c) They're the only SuperSprint dealer in England. Meaning, they've been making tunes for 130s with SS headers for a long time-- they know what they're doing there. I doubt AA has done a single DISA enabled header car yet, much less tuned one on their dyno to see what works and what doesn't.
(to your above point, yes, header tunes are significantly different-- e.g., the only hardware difference between the US spec and euro spec e46 M3 is headers, yet the tune differs in VANOS timing, AFRs, timing, everything. Significantly different tunes).
d) the Evolve cable is also a code reader and clearer, that displays the codes in plain english
e) Evolve seems to have a better handle on modern BMW ECUs-- e.g. AA has blown up a couple SCed e9X M3s in their development process. Evolve has not in theirs.
f) As far as I know, Evolve is the only tuner that can disable emissions systems and still leave them showing as "ready" when plugged into OBD2 readers.

Not ever a little bit of a tough decision, imo.