I went with OE cats from the dealer. There are a load of posts about whether to go for dealer or aftermarket and the general consensus is dealer.

It can be very expensive if the cat has broken up and somehow gone upstream into the engine.

I'd be surprised if bad fuel were to blame. In 15 years and 300,000miles of motoring I've never encountered really bad fuel. Plus, petrol stations and pumps are pretty heavily regulated these days.

__________________
JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190