Definitely a Titan and as far as finding the rare materials just make sure you have a ghost shell that marks that material! For me I think the best way to do it is solar-Titan, arc-Hunter, void-Warlock! I did all 3 on my Titan (side note, do not do void with a Titan if you want it quick!!)
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This guy knows!! Ghosts with perks for finding elements can be bought at the tower from Lord Shax, if you don't already have one that spots helium