The only time I play it is if there is decent competition in the lobby, and if I have stuff small stuff I might need to do around the house which if I lose, I can go do them for ten minutes or so until I get back into the king match. Otherwise, I have a lot of problems with the KOTH system.
The lobby interface has some downfalls. When you become king, whichever menu tab you were last looking at on the right hand side, (players, stats, or chat) is the only one you can look at until you either lose or everyone leaves the lobby. So if you happen to be looking at the chat and then you get put into the king match and win, then you can never again which person comes or leaves the lobby until you lose or everyone leaves. Or in some instances, if it is on the players tab when I become king, people are sending chat messages and I want to see what people are writing...and maybe even respond if they are talking some smack!
I don't like how you can be the king for awhile, but if you want to leave the lobby, you have to take a loss unless everyone else leaves first. Lets say you win 20 straight games in KOTH, and are getting bored of the competition in the lobby, but in order to leave you have to take a loss. I just feel like the king shouldn't be required to take a loss once they win 5 or so matches.
Ultimately, the lag is the biggest issue. nearly every time a new person joins the lobby or leaves the lobby, the match will lag. This is just very annoying.
In terms of competition level in KOTH, I think the best thing to is join a room. and scroll down the list of people in the room to see who is playing KOTH. It is nice to see how many people are in the lobby and which people are in the lobby (including their 1v1 record and player score) and pick the lobby which is suitable for for your desired competition level.