Originally when I chose SmartThings, it was because they supported Windows Phone (which I had at the time). The other factors to me, which are more important are...
1: VERY OPEN - There's an active community that work to get devices integrated into ST.
2: Supports multiple standards (ZWave and ZigBee)
3: Works with a TON of 3rd party devices such as Amazon Echo, Harmony Remotes, IFTTT, etc.
So, I don't know what other "other system" your considering, but SmartThings is the most flexible IMHO.
As for v1 vs v2 - If you come across them they should say v2. V2 has a squarish look to it and there's a battery compartment on the bottom. You want v2 IMHO. But if your looking to save a couple bucks, then get v1