It seems everyone else is focusing on a melee duo team, and following that, I'd propose RDM/PLD + DRG/BLU: it's freakin' sick. DRG/BLU gives good damage output, ridiculous healing capacity (basically bottomless healing as long as they're refreshed). RDM/PLD gives good damage mitigation/hate control, decent damage output, and a slew of enfeebles to cripple any monster, not to mention emergency cures, Refresh for your DRG, a mini-Invincible* every 5 minutes (obviously when used with Convert, you can get a safe vert-under-fire while also getting some nice spike hate from double enmity Cure IVs), and a JA stun.
Not to mention Death Blossom > Drakesbane = Light.
*As in, the mob would need to be hitting you for (Phalanx DR + 1) * 10 damage (250 damage with a 24 DR Phalanx) normally to damage you at all at the beginning of Sentinel. A normally 500 damage attack would deal 26 DMG, etc. The effect does get weaker over time, but is easily enough to make your SS last through your Convert + Cures.
A very situational setup^^
I can't speak for everyone, but I like to low man as much as possible. This includes all situations, not just special circumstances. The main problem with DRG/mage soloing is their total reliance on their wyvern pet to heal them. Long time ago back when I first began playing FFXI, I noticed a disturbing trend. DRG's are not very AoE friendly one bit. All it takes is a few bomb tosses or another form of nasty Aoe and say goodbye to your wyvern for 20min. I might add that most attacks that go though shadows often wreck havoc on a wyvern. Our DRG in our Nyzul static really hates Flayers, frogs, and those **** chariots.
Frankly our best duo partner is another RDM. You might take longer to kill sometimes, however it's the safest best for success across the board. In a non-situational duo, other jobs can do ok. THF is a good tank if they are smart enough to steal your hate. NIN/dnc can solo almost anything by themselves so a RDM partner just helps them along. There is no ideal partner for all situations, you just have to adapt and hope it works.