I would avoid live fish altogether as everyone before me has said. I also think pinkies are not a complete diet due to low to no calcium. I feed mainly rodents with the occasional Silversides/nightcrawlers and give a 50/50 calcium plus multivitamin mix 2-3 times a month.
I'm in the process of experimenting with breeding gambusia and treating them for parasites to see if it can be done and will be feeding 3 garters them twice a week along with pinks.

As for a recommendation for a garter. Imo radix have the calmest demeanor and best personality. Concinnus are another sure bet cause they do alot of basking and barely use hides that are provided so you will see them alot more than other garters.