Aside from limiting your selection based on projectile speed, I'd just say use whichever codenames you like the most, be it effect or performance based. On my freelancer I'm quite partial to Claymores. I'd say the "best" codenames are those you're best at using (if you prefer faster or slower weapons, for instance) or enjoy using the most. I believe the wiki has pictures of most of the effects on the weapon pages which will save you some time and money in choosing if that's what you're interested in.
At the end of the day though, almost all of them are good weapons; but it's the skill of the pilots using them that makes them effective. The most effective loadouts and ships available don't give that much of an advantage over a better pilot. While an extra 20 points of damage per volley is certainly nice, I doubt it's very often the deciding factor in a punch-up.
(Although, that's quite rich coming from me, who monumentally sucks in a fight:D)