I am not a dev and we are investors in Apsalar so I am already biased, but our reference calls with Devs made us comfortable investing as they had tested Apsalar's product vs others and gave many compelling reasons why they were choosing the Apsalar platform. I think this Quora post does a great job of comparing mobile analytics platforms for iOS:
Some friends at medium sized mobile game publishers ran both SDKs at the same time (without either providing much of a performance issue) but said that Apsalar was clearly the winner because of cohort analysis, event settings (built in ARPU per game/custom tracking), and cross-game customization. Haven't tested it myself though so do your own diligence.
http://www.quora.com/What-is-the-best-Mobile-Analytics-servi...