Having been to Leeds for the past three years, and also having been to Glasto, I feel well qualified to answer this question.
And the answer, ladies and gentlemen, is GLASTONBURY!
Yes, the 'Festival Republic' weekenders usually have great line ups. And they've always been so much fun for me, I'm not bashing them at all because I *do* love them. However, the crowd is generally 'young' and a fair few people do behave like absolute tits. Plus, everything's expensive and generally a bit rubbish - there's little to do other than get bladdered and watch bands. Hey, that's ace, BUUUUT...
Glastonbury also has an AMAZING line up. Main Stage isn't always fantastic, but the fact that there's well over 30 stages means you will always find something to do. Some bands will play about 6 times over the weekend, meaning you WILL get a chance to see them at least once. Clashes aren't that horrendous. The place is big, and absolutely beautiful to see. The views from stone circle and all the flagged places are gorgeous, and some amazing sunrises/sunsets. After the headliners are done, there's always Trash City and Shangri La, and loads going on all over the shop. Noone blow things up. The drinks are decent (spiced apple juice = £2 a pint.. 7% Brothers pear cider.. etc) and the food places, if you can seek them out, are far superior to Leeds. Square Pie company for a start! Glasto is just so, so much better than any other festival I've experienced. There's something for everyone, little/no hostility and possibly the best thing is being able to take your food and drink with you to bands. It's cheaper and gosh I could rave about it all day.
Glasto > everything, ever. As my signature says.
Seriously though, I cannot express how amazing Glastonbury is. Everything to 'do' - wheels, rides, face painting, crafts etc- is free once you're in.. it's brilliant. Just go. You'll never regret it.
I've got my ticket for 2009 and I'm bloody excited already...