I tend to get approx a year from a set of 4 tyres, which is around 15k. But then I demand some level of grip.
Ones I would really avoid personally are any Michelin (no grip after about 3 months), any Avon (no grip and poor durability (managed 4k out of a set of rears)), and whatever junk chrisgixer had on his last year (I refused to drive his car again until he changed the tyres)
.....and the winner of the worst tyre award is, q fanfare....... falkn 912, like driving on a water bed 
You should try the no-name rubbish the previous owner fitted to mine.. going round roundabouts makes you feel like you're in an American movie - no matter how slow you go*, they squeal like stuck pigs!
* OK, that's not strictly true.. you just don't have to be pushing very hard at all.
I get to drive a fair few Omegas - I am very fortunate in that way. OK, I know that day when I drove chrisgixers at Asheridge, its a fairly bumpy country road, but it was dry, warm, sunny day. I would say that car was dangerous. Very dangerous. No telling which way it was going to veer. Slapped my (very worn) Dunlop SP9000 (a tyre known to tramline badly when at the end of its life), and it was noticibly more stable.
That tyre is lethal on Omegas.