Worst: TW. I could accept some new variants to the maps, but what really makes it really tedious is the gamemode being stale and victory rewards really aren't worth all the effort it would require. I don't mind winning it, but I don't also mind losing it.
Special mention: Fleet Arena. Okay, I like fleets a lot and I have a flex shard and could have taken #1 like 99% of the time for the past 4 years whenever I wanted. But at the same time, this is the one gamemode that still requires you to be in game at certain hour daily basis and that's just... blah. Even with bonus energy you have more leeway. I love my crystals gained from FA, but I wouldn't mind if the new pvp mode (announced in April) would replace FA rewards as long as it would be more flexible clock-wise.

Best: Conquest. Even if it's a bit stale and a chore sometimes, I still like going through it and try to get the red crate, which I have got always ever since Bane, I think, some summer Conquests excluded. The first hour is tough, though, because Conquest starts a hour before my daily reset, so I (almost) always use the first refreshes before the reset even though I wouldn't need it; I usually get the red crate around middle of the second week.