for me, my UWATEC com, I have been using for 4yrs +, abt >150 dives, till has 3/4 of the batt life left. Somemore, unlike sunnto, which is always ON, which drains batt life much faster, UWATEC only starts when it touches water. It is water activated, it uses batt life only when activated by you or when it touches water. So, the $200( I know it sounds troublesome and ex) but if you put that factor into account, it all boils down to one thing.
Sunnto: more ex, more conservative, smaller, more stylish, can be worn as a normal watch, drains more batt life, some models known to spoil easier. No fixed distributor (only one and damn ex), so warranty is also quite questionable if you get cheaper sets(parellel imports)
UWATEC: big, bulky, not nice to look at, batt lasts longer, less conservative, lighter, distributer is Richmond(so warannty is more promising), more changeable parts(eg, com display cover, strap...), no time stamping, lesser functions, slightly cheaper, lesser dive info availible(based on my model, ultra pro)