i) Lithiums are prone to runaway overheating;
ii) The Lithiums are more expensive
iii) They appear to be more sensitive to overcharging with catastrophic affects; and,
iv) They cost a lot.

I'd get AGM's if you have the room. They are less sensitve to overcharging, while you don't get the warning (if you're looking at the fluid levels) they seldom fail catastrophically within normal alternator and charger ranges.

The gel cells are fine -- but they are a bit more sensitive; and, the outgas a little if challenged. IF YOU DON'T PROVIDE SOME VENTING and that happens, then you can get a hydrogen induced fire. A few years back, Hinckley had a sailboat that burned to the waterline according to a Marine Electrician (Bob Campbell, in Annapolis).

I think Maine Sail's suggestions are spot-on.