I've got BJ City Select and love it, highly recommend it. I bought the Maxi Cosi which is the best capsule to use with it - clips in quickly and easily. A bracket is supplied with car seat adapter kit so it can be used with several other car seats (you may be able to get the full list from the BJ website) however it's more fiddly using the bracket. Would you consider hiring a Maxi Cosi or buying one?
I think my husband would kill me if I bought another capsule, I had a hard enough time convincing him I needed the one I bought because dd2 is our last baby. Hiring isn't an option because we live to far from any place to be able to pick it up. Baby jogger are now making an adaptor for a seat called the britax b-safe which is the American version of the capsule I have. I think I'll email them and see if it will work with my Australian version of the seat as well.

For those that have the city select do you find it hard to push with 2 kids? Especially with toddler at the front. Living in a small town not everything is smooth and I'll have a lot of uneven surfaces to push along and I'm a weakling.