Hi there Fox
I run both Voyager and StarMap Pro. Quite frankly I don't like StarMap. I find that it's too "itty bitty", and ponderous to navigate around in. Settings are a right royal PITA. Also, it's "WiFi" setting seems to do absolutely nothing - it doesn't even detect my home network 802.11 modem let alone the SkyFi and gives "No networks detected". Don't know what it's trying to do.
Voyager is a pleasure to use, and most functions are very similar, and some better then the equivalents on StarMap. Granted, SMP has many more than Voyager, but I find that i don't use any of them, because they aren't much use on a device the size of a phone - and it is still a phone after all. I'd rather use my laptop. photo exposure timers and logbooks are basically useless to me on a device like this. All I want are a good planetarium, a way to search for objects and a nice smooth display - which I think that Voyager just does better. Coupled with the SkyFi it's a killer combination now - very powerful indeed.
While SMP covers 2.5 million stars and 13,200 deep sky objects, Voyager only covers 320,000 stars but - more importantly - 18,500 deep sky objects, a full 5,00 more than SMP.
Here's a decent survey of iPhone planisphere apps - but is outdated and doesn't test Voyager (especially the latest version, v1.3):
http://physics.weber.edu/schroeder/iPhoneStarApps/