+spd -lck seems most common on normal/hard mode. it doesnt matter what u do tho. just go with what u want. if u play lunatic or lunatic+ then it is recommended u go +def, but there is no point playing lunatic in this game.
They affect base stats, growths, and max stats. Each attribute chosen might also affect some other stats to a minor extent. http://serenesforest.net/fe13/char_growth_all.html http://serenesforest.net/fe13/char_max_all.html