Closed, IMO, there isn't much difference in carry - both are fairly flat, solid but not overly heavy, with good clip design - the wire clip WILL shift more than the solid clips, but grips very well and is a much more low-key. Of course, being Spyderco's, they are somewhat wide.
Lava is heavier, shorter blade, more... ergonomically neutral handle - should fit in ANY hands. Points very easily. Opens smoothly, good lock-up as with all Spydies.
Salsa is a superb knife, light -- wide, thin flat-ground blade. The hood makes it open very easily, even with gloves. The grooves in the handle happen to line up well with my finger-palm configuration, but may not for those with much larger or smaller hands. However, it really isn't that big a deal except for hammer-fist grips. The compression lock is superb - it also results in a larger handle to blade ratio, though not as obvious as with... for example, the Paramilitary.
IIRC, the Salsa uses AUS8 (except for the Ti version) while the Lava uses VG-10 for blade steel.