I quit playing the dh tank aswell. Boring af. DK's tanks are really great for solo, be it lfr, group, m+ anything. You have 2 differents dps spec that are close enough dps-wise and a tank that can self sustain by quite a lot (don't be surprised if healers don't like us though, because I feel like DKs tank are likely to be the most spiky).
I have 4 tanks : DK, BrM, Warrior and DH in specific order for the most fun. But I'm probably biased. Tried pala, but couldn't really like it. I guess it has something to do with blizz and their love to the FOTM classes ? I'll never know.
One thing for sure though is that 20 ilvl make a lot of difference. You should probably redo your class quests to be sure to be able to get at least 3 relics for your paladin. Your DPS will definitely increase.
I don't have a paladin @ lvl 110, but for what it's worth, sco says that paladins are currently ranked very high, just behind druid while DKs are ranked last. But they're all close together really.
In the end, pick the one you're having the most fun with. I picked DK because it's simply my main and I know a lot about this class, and monk because it's a very dynamic one. Warrior with the current devastator's talent can do a lot of damage aswell but they suck at self sustain and if I recall correctly, their ignore pain doesn't scale well the further you go up in ilvl.