As for incubators, I think they're the only thing worth spending coins on! Sure, you get a lot of crap, but it's totally worth it for the good ones you get every so often.
Currently?
I think Aerodactyl (which haven't been too rare in tie wild for me), Lapras and Snorlax (still don't have one) plus miltank from gen 2.
Dratiniand larvitar seem roughly equivalent, though apparently dratini is rarer, now, so less scope to ad to the awesome dragonite population - still not fully powered up my first one!
Oh, and mareep. DS1 finally caught one, the other weekend, but it never spawned for me - bad timing as we were in a moving vehicle.
Given the vastly enhance likelihood of hatching a crap unevolvable over a good one, or even a good evolvable, I'm now happy to stick the 10K eggs in my free incubators, only.