Which Pokemon do you guys prefer for HO teams, TR Slowking or RD Kingdra? Both are good late-game cleaners and check rain teams. However, Kingdra can actually outspeed Pokemon without set-up, needs no set-up in rain, has better all-around coverage, and fairs better against sun. On the other hand, Slowking is one of the best checks to Keldeo offensive teams could ask for and can generally serve as a pivot in all stages of the game thanks to Regenerator (this is huge in comparison to Kingdra, which you usually try to keep safe until late game). It also has less trouble sweeping through rain teams after setting up TR, thanks to its ability to OHKO Pokemon such as Keldeo, Toxicroak, and Tentacruel, all of which can prevent Kingdra from cleaning if not sufficiently weakened. Finally, Slowking is less priority weak than Kingdra, thanks to HP investment and resistance to Ice Shard and Mach Punch, meaning it has much less trouble sweeping when priority users are alive. (Slowking also can act as a check to TR teams which usually trouble offensive teams, but this is really minor)
Both have its pros and cons and i feel that they are both equally viable options for HO teams, even though TR Slwoking is criminally underused and underrated compared to Kingdra (which is a bit underrated too).