I use the Bioresearcher kit, a Pule Rifle, and a Split Beam rifle. This may or may not change with the 45 day patch, we shall see...
As science you want to try and maximize you exposes then capitalize on them with the Split Beam rifle. One on one I usually open with Stasis Field and then drop as many expose chance abilities as I can on the player. If none of the abilities proc an expose, then I use the pulse rifle on them and switch to the Split Beam for a shot...you can save the Split Beam if you want for the next cycle of expose chance abilities, but it usually doesn't hurt to put a dent in their health and just battle it out.
When against a group, I put Stasis on a player that is off to the side and not likely to get hit by a stray shot. I then unload my aoe expose chance abilities on the mass and hope for the best. Always be sure to fire the Pulse Rifle or other expose weapon first to either soften up the targets or open up more exposes. Also, be sure to focus a target that at least one other player on your team is targeting.
If you are alone, then I suggest backpedaling a lot and throwing expose abilities. When one procs, drop down to one knee (if you are outside of melee range of enemies) and try and pop the player you exposed, then quickly get back to moving. Sometimes you will have to leave an exposed target behind because the other players might be too close for comfort. Tachyon Harmonic is a great ability for knocking away close enemies and buying some time though. If you feel you have the time, feel free to shoot off your expose weapon at the oncoming players to try and get a lucky proc. If the enemy has roots though...well, good luck.
if you haven't made the science toon yet, i suggest a ground trait (telepathy/acute senses) or any of the spieces that will allow you to see stealth. This will allow you to see tacticals coming for you miles away in their operative kits. Also will be +++ for the blue team, as the usual PUG has no players able to see stealth.
Just remember tacticals are not the only class out there.