The
IDB forums are great. There's a forum called "Weapon Advice & Comparisons" where anyone can start a thread and then some more experienced IDBers will offer weapon set and training advice. They helped me a lot when I was newer to the dome, and now I'm one of the people helping others.
Siniri, at first glance I'd say the mynci, because its level is high enough for the faerie ability sink and the other stats are pretty balanced. It still falls in the 21-40-level range, so can be trained for two codestones/three hours per point (and yeah, alternating the academy and the training school is a good plan). Str/def should be brought up to at least 55, and hit points should be higher -- just follow the training guide in my above post as best you can. However, you could also use the lab pet if you were committed to keeping its stats balanced and not letting the lab get hit points out of hand.
Whichever pet you choose also needs the abilities burrow, sink, and drain life, at least (I like regeneration/restore/healing vapour -- pick one -- once you get more hit points, too, and fiery gaze or diamond dust are good, as they have a chance of freezing). I think you (and anyone else who wants set advice) should register and post a thread at IDB for much more help.
