Really depends wich pets you have. My merc's medic gets stimulant with the 2nd upgrade, not that fast spamming power but he keeps a few nonstop protected.
Even tested around with it, he come rushing to you when you get mezzed and puts stimulant on you 
The heal of Aid other is pretty enough to get my lowest pet full health again with 3 slotted heal. Also great in teaming with a brute (or sortlike), the bit of heal makes just the difference.
As for Acid Arrow, the aoe-range is pathatic small. Luckely the gunbursts of my mercs add a bit of extra def-debuff making them hit a bit easier. Currently going 2acc on the lowest 3, 1 acc on both specs and commando, they hardly miss (fighing often +1 max).
50)Sinergy X/(50)Mika.
(50)MaceX/(50)Encore
Sign the petition, dont let CoH go down! SIGN!
Actually, I'm lvl 45 and I love Aid other.. this nice little heal which keep the Assault bot alive when Repair is not recharged and you protectors are busy spamming Photon grenades 
I would have thought Stimulant more useful at level 45 - mezzing more ouchie than damage, but I bow to your experience on that!
[ QUOTE ]
[ QUOTE ]
Stimulant and Aid Self
[/ QUOTE ]
I would take Aid Other instead of Stimulant.
[/ QUOTE ]
Why? Heals are pretty useless anyway at level 30+ IMO, and particularly one I cant use effectively in combat and (with A MM rubbish HP) one which wont be very powerful. Id far rather have stimulant to protect my robots from mez attacks.
Admittedly Heal Other feels better a low levels, but Im playing this one for the long haul.