triggers isnt the oposite of JASS, triggers can be JASS and GUI. but ehm, JASS is only better if the spells r complicated. with JASS u can make spells multi instancible and it has less leaks (well i heard) but u can clean leaks easily with GUI to (go dl leak checker on this site)
There are really only three reasons why you would want to use JASS over GUI. Number one is to make your triggers more efficient. Blizzard made almost all GUI functions more complicated than they should be and thus they cause more lag than they should. Also, those "if-then-else" loops can also be made more efficient by using JASS Number two is that you can't create/manipulate local variables with GUI. You HAVE to use JASS, and local variables make things a lot easier to work with (and a lot more efficient). The third thing is there are some functions that simply are not available in GUI, so you HAVE to use JASS to use those functions.
If your spells have a LOT of special effects/lightning effects, make units do crazy things like knockback and jumping, and you require multi-instanceability, use JASS.
Ramza - if you're not lazy/incompetent/an I Dont Care person/n00bish, you DO use JASS
also, JASS is much faster than GUI ( if you can type at a competent rate ) to write, and has many features, (such as X/Y functions) that gui does not bother using
oh, and aznricepuff, to add to your list, GUI loops suck
I personally using GUI triggers with custom JASS functions if necessary, because GUI is much faster for me (making what I want) and I have enough programing in my job, so I prefer clicking:]