i just got a 1991 civic hatchback, but i just hate its lack of horsepower. an engine swap sounds like a good idea to me but im not sure whether i should use a b16a2 or a b18c5. a k20a2 seems a little too expensive for me. any ideas? please help  

if a K series is too expensive i recommend the B18 then still gives good HP but in a low cost.

but if can just save up for a K20 dude its alot better than the B18  

it all depnds on how much you can spend on top of the engine price you'll have to take into consideration the price of the swap unless you can do it yourself  

i'd look into an used K20A.  You should be able to find good prices for one in good condition.  If not then a B18 from a GSR or B20 from a 99 Si would be my recommendation.