Good places to use guthans?

Fire Giants (under waterfall or in Brimhaven Dungeon)

 

Ankous

 

Bandits

 

Daggonaths (under lighthouse)

 

Random Slayer tasks.

 

 

 

The main spots I have used and seen people using guthans.

dragnnoths are my fav on that, and fire giants are great as well, but id suggest on slayer tasks, i only really train combat with slayer any way- that way u lvl more skills at once

It depends on what you're looking for, but if you're going to be training for hours on end & want to pay minimal attention to RS, you can't go wrong with bandits. They tend to be crowded, though.