You mean, which one to try first? Well, you should probably understand that wanting more bite and attack is about your tone. So it sounds like you basically like your tone, but would like more of the 1 to 3 kHz frequencies which add clarity and articulation to your picking, which can make your sound more aggressive when used judiciously.
Sustain will be improved by either a boost or an overdrive, but the overdrive will add noticeably more. OD's add in harmonics and light amounts of distortion to your sound which are an important part of overall sustain.
An OD will definitely tighten up your bottom end a lot more than a boost will, especially the Tubescreamer types of OD, since boosts will actually be providing more of the original signal of your guitar. If your guitar produces a lot of bass frequencies with the amp set the way it is, a boost is going to produce even more, since it boosts the entire frequency range of your guitar's signal. That means that boosts don't really do much to tighten up the bass directly. What they do is make it so that you don't have to run your amp's gain knob quite so high, which will reduce the bassy mud that the amp produces. OD's generally provide a slight cut in the bass frequencies directly, and depending on the model, will otherwise provide anything from a generally transparent to pronounced mid-hump signal.
Just FYI, treble boosters, which are yet a third category of front-end signal boosters, cut bottom end and really amp up the treble frequencies to provide a very creamy, high-sustain lead sound. Treble boosters can also be used in conjunction with OD's if you place them in front of the OD. I use this setup all the time and it can turn even a Triple Recto into a harmonically-rich, singing sustain monster for leads and solos.