If your pet shops have green water quality in the plant tanks dont buy plants from them, sounds like they dont maintain them well.
Plants in general will not change your water colour(some mangroves, bogwood, can) it is the algae that will produce the green or funky colouration. Plecos and Cories, as well as guppies love to have cover: it depends what you are looking for:
I keep Spiruana, Minature Sword, A maroon crypt, pink baby tears and a broadleaf which im trying to find a name for.
It also depends on your lighting: more exotic plants require more specialised lighting, and some go so far as to require C02 injectors. If you want a low cost plant that fills your tank and gives you plenty: go Elodia. If you want to have plants that are a little more expensive but far prettier: see what you can find at a non algal fish shop.