The Princes are insane. Sans Dancer and SoC, their movelist is longer than any 3 bosses in the game, and I'm pretty sure they have like a triple damage type split. The RNG in that fight feels absolutely unfair. Zwei is a good choice though-- it can hit both princes in the last phase. I used the Greatsword the first time.
Armor is another matter-- I've dumpstered him first try in three playthroughs. Dancer just fucking tilts me, because the timing is wrong. I have trouble with Dancer, Princes, and Nameless-- who I'm stuck on with a fat-rolling STR character. He feels very Ornstein-ish, I just can't keep my stamina up enough to finish him. I expect my Quality will be the first to beat every boss, move into DLC, and NG+. That was what I did with DS1 and DS2: Scholar: Company of Champions. Great balance between DPS and DAM, great weapon movesets. It's really the way to go-- though there are excellent weapon enchant builds favoring the margins.