You will get a huge range of answers, and none of them may be right for you.
Right now I could make some guesses...
- You're using an underpowered amp playing with loud guitarist(s) with big amps and a loud drummer? No need for pedal, need for bigger/better amp
- You're playing a P-bass with flats, but trying to sound like flea? Get a stingray, not a pedal
- You want a tone-shaper - might need a pedal, I'd suggest trying out EQ's, compressors, Sansamps, and seeing what you like.
Tell us what you're working with (what bass, what amp), what you're working to/against (what other instrumentalists are you playing with, what kind of instruments and amps to they have) and what you're working on (what style of music). Clips (or references to particular sounds in particular songs) of what you're aiming for might be helpful too. Then we may have more helpful suggestions.
Steve