The primary benefit would be that you are going to find a LOT more Tin than you are Gold. So if you are looking for XP, go for the common metals.
[EDIT] Tin, Iron, etc... sorry if i confused anyone... I've gotten asked a lot in-game lately about tin. Point is, if you are training a skill, mine something common if you are wanting to gain XP. I you are looking for trias, go for the exotic metals.