I'm a BIG fan of Sips and Sjin and I also love Martin's channel. I used to love Simon and Lewis' channel as well, but their content lately has left me wanting for more Minecraft lol I have no idea why they abandoned their FTB series. I really used to like it. At least Sjin kept FTW alive, though he should focus a bit more on his Let's Build Erebor IMO
Huge fan of the Civ 5 series' on Duncan's channel, Sips and Sjin are hilarious, as are Simon and Lewis. I'll watch the odd video on any of the other channels, but not as frequently.
You should give InTheLittleWood AKA Martin a try, I love his accent and he's really cute His GTA5 videos are supper fun and his WindWaker HD is very fun as well. EDIT: Oh yeah, "An evening with Sips" is usually awesome and hilarious too.