Thought Bubble is great! It's almost exclusively an artist thing so it has a great vibe, but even though the competition was really strong it's got good enough attendance to still make good money (though it's never going to make you megabucks, just good money). Go to this to network and make friends as well as pick up some sweet indie comics!!!
Besides this, it's really really well organised- they engage amazingly with the local community and advertise months in advance, and have an anthology that's distributed to at the very least UK comic stores. Venue is very close to the centre of town with lots of nearby hotels. Some people don't like that it's split over 3 separate halls but the traffic between them is fine as each bit is well signposted and there are loads of staff. Basically no complaints, though because of it's popularity it is juried so it's not always possible to go (though they've let me in both years I applied) but this is done in March-April so plenty of warning. I would recommend checking it out as an attendee first if you can, just because it's a very unique event and I feel like doing this myself really helped.