I'm not a big Tac player but my strategy for my Tac chars is to use Phasers until high enough to use Anti-Proton weapons. At the upper levels, some enemies wouldn't be affected by the subsystem shutdown and in PvP most players would have resistance against phasers.
About the worst you can use at endgame PvP is plasma weaponsatm, since everyone runs STF shields, all with plasmaresist.
I still use Phasers for RP reasons, but then I don't PvP at all anymore because of all the ridiculous spell casting consoles that pervert the matches...
For DPS types Antiproton might indeed be teh best choice, go wfor AP weapons with High Accuracy and Critical Chance buff.
Phasers are probably best for a tank, since he can't do any damage anyway, but the phaser procs in combination with fire at will might wreak a little havoc. Or go with Disruptors to lower your enemies damage resistance.
A Controller will generally be best suited with polarons to reduce energy levels.
A Debuffer needs to run Disruptor or Tetryon.