internal security has the highest % of kill misions i think (97%), can't speak about the pay differences though, if any. there is a skill in social that increases pay by 5% per level btw, can get it to level 2 fairly quickly for a 10% pay hike
avoid 0.1-0.4 like the plague (0.5 still is safe), just come out to 0.0 space with us once you can fly a battlecruiser half decently. also join the tribalwar channel ingame, almost always some people on to answer questions/give advice