>>497118387.5: Smallest roster, much higher execution requirements, doesn't look different enough from 10.5 or 12.3 for some people
10.5: Practically an older version of 12.3
13.5: Netcode makes it unplayable, game balance is completely broken, and a lot of people simply don't like the floating mechanic
14.5: Same as above but slightly more balanced
15.5: Gameplay was mostly fixed, netcode has been improved significantly with fan patches but it's still rough
Really there aren't many options besides 7.5 and 15.5. The former is probably the hardest to get into and the latter is simply a worse online experience, even if you like/don't mind the floating mechanic.