Mission is rather small, I'm not sure it can be subdivided further into communities.
In general I recommend the block delimited by castro st. on the west, valencia st. on the east, market st. on the north and 24th st on the south. The parts west of mission st. and north of 24th are more sketchy.
I would suggest investing in a few day stay in SF to check out various parts - after all what is sketchy to me might be colorful to you (or vice versa) i.e. you can't assume that your taste will match the taste of people giving recommendations here.
In general I recommend the block delimited by castro st. on the west, valencia st. on the east, market st. on the north and 24th st on the south. The parts west of mission st. and north of 24th are more sketchy.
I would suggest investing in a few day stay in SF to check out various parts - after all what is sketchy to me might be colorful to you (or vice versa) i.e. you can't assume that your taste will match the taste of people giving recommendations here.