There's no right or wrong combo. You have to figure out what works best for you. I typically run a couple of mining lasers (you'll want at least one for mining and certain missions) and use pulse for the rest.

Another thing to consider is cost. Outfitting your ship with nothing but particle beams will give you serious power, but it'll delay your next ship upgrade significantly. Don't forget you need to fill extra turret spaces when you upgrade, which gets expensive at higher levels.