I'd probably go with the Clan ER Large laser to be honest. You out range pretty much everything, its small enough that its going to fit in just about everywhere, and its going to fit in well with regards to heat and damage with whatever you're replacing. Okay, so its not on the list, but I'd probably go for that. :)
The HLL might be an obvious choice, but the to-hit modifier and its range brackets don't make it an all around general purpose weapon IMO.
The HPPC, if you're forgive me, is a little too heavy to cram into a design easily. You're really going to have to work to fit them in where they're not designed to be, and you're going to have to give up alot to put them there. And if you're dealing with the Sea Foxes, why not go for Clantech?
The IS ERPPC is a solid general purpose weapon. Sure, its high heat, and the damage is the same as the standard PPC, but if you don't have the Clan version, its a good design, and the range on it is the same as the Clan version, so atleast you can shoot back. Its also produced in bulk and alot of designs already have them, so you'll have less trouble cramming it in. But again, if you're dealing with the Foxes, why go for the IS tech?