rock crabs? they have 50 hp each. Drop a good amount of gold charms if you train summoning. If you are f2p try seagulls in port sarim. They have the same hps as cows but can only hit 1 very rarely.
bronze if you are at a lower defence monster ie. fortress guards/fleshies. Iron if you are at mossies or hill giants. stay away from mith and addy arrows.