Telvanni robes look the coolest and actually work with the Mage Armour unlike the Vampire Royal Armour.
If only they didn't have the handicapped effect that most cool looking robes have I'd be for them as well. Although, if you can overcome that flaw go with them.
*Personal note to Bethesda* Either give us non-magical robes or boost the effect to be actually useful. Even if it's just a 125% magic regeneration I found that to actually be useful to an extent when combined with a necromage/vampire and the ring of erudite (or however the spelling is) --- "Screw the rules, I have money!!!"