Gumiho as critical damage. Thats one advantage. That's it.
Sweet angel has HP and Max physical/magic damage, wich is two advantages.
Well, since we are talking about Engineers, I'd say Gumiho because engineer have equal HP/MP/STR/LCK wich they can upgrade trough MISC skills, and since they will need to grind alot, critical damage is best. But what'd recommend is both of 'em. Sweet angel for bosses and mobs, Gumiho for grinding.