I have to say that if the manga doesnt have too many chapters or isnt finished, its better to wait. Just look at poor Yumekui Merry which got a crappy second half of the anime which was anime only. Sometimes they manage to pull off good anime only endings or stories, but most of the time theyre just crap. I dont know how fast things progress in the manga Dalliah linked, but i'd say Arachnid atleast could make for a good anime. About 1-2 chapters per episode. Its up in 24 chapters right now so that'd be 12, which is enough for a season, and still have a good pace.
Its worse with manga that doesnt progress too fast from one point to another (i feel the need to mention Bleach here. One chapter barely covers an episode).