Initially I hated Tediore guns because as a habitual reloader I was literally throwing ammo away constantly (if you hit reload before the gun is empty you get a better "grenade" effect but you lose all that ammo - especially if there's no one around to throw the gun at) however as the Siren I started to embrace Tediore weapons - basically you want to do as much damage to the target while he's phase locked as possible, so you tend towards high clip sizes, high RoF and quick reload times, but with a Tediore gun you get to throw what is essentially a weak grenade as a part of the reload, so it's great for maintaining damage on the target.
I like joining games where the host is a level above me because in addition to the average quality of the loot being better purely for being a co-op game, the loot is skewed slightly higher anyway because he has an extra level on you.
I just respec'd my character to be more of a healer for co-op. It's so hard to choose where to go at lvl 20. It would be nice if you could save respec builds for quick switching between a co-op build and a selfish single player build.