My advice? Give 2nevets a holler and see if he can tell you what's on it right now, then see how you like it. That'll give you a reference point to decide whether you want to go thicker/thinner/brighter/warmer, or just what to buy again, if you dig 'em.
As far as electric strings go, nickel is warmer and stainless is brighter, flatwounds tend to have a much quicker decay (musically speaking, not longevity-wise) than round-wound strings. There are a lot of guys that grew up in the '60s (like my dad) that will dismiss flatwounds as dull and lifeless strings and a lot of the old ones were, particularly b/c nobody ever changed them and they were all you could buy. IMO, some of the better quality ones out there now (e.g. D'Addario Chromes) are still pretty lively strings, with a nice spanky/snappy response.