I have 21st century and I can tell you that I've had 4 claims with them. 1 went well and 3 were pretty bad. In the end I got a decent settlement each time but i had to REALLY haggle and everytime they lowballed me big time. When my 91TT (4 out of 5 condition, 90K miles, all options) was totalled in 2000 they offered me 9000 and tried to tell me that I had no choice in the matter. When I b*tched and told them pop's is an attorney I was looking at 15K the next day. I had a stolen 69 camaro which is hard to judge since they went by blue book and naturally I had a lot more money into it. It was a pain and I didn't get anywhere near what I would have had to pay to buy a comparable car. They stalled and I need the money so I took it. The last claim was recent (another totalled car - yes i have bad luck and no it wasn't my fault) and after about a month of letters they almost tripled my offer.... they really do lowball.
It's the only insurance I've had so I don't know if this is normal procedure but they definately didn't make it easy. I wouldn't reccomend them. The only good thing was my premiums never went up.