What I do is wait until I have my final gear, then only put in Gold Charms. As for the particular type, You can't go wrong with Gold +100 vitality charms.
If it's a choice between +Vitality and +Mana or +Constitution and +Intelligence of the same colour, go for the +Vitality/Magic and not ones which boost the CON and INT stats. The stat charms give a bonus of 10 to one stat, which is great, but it will always be less then a direct bonus.
Resistances are pretty easy to come by, and can usually be ignored.
