I’ve tried out a lot of ROMs in the last few weeks. Cognition was a great ROM, but is no longer actively developed, the developer having moved on to Perception. Perception showed a lot of potential up to and including build 4, but all builds after that have been unstable to the point of unusability. Axura CE (Captivate Edition) showed promise, but then some schoolyard drama appears to have killed off that project.
But the ROM of the moment and a serious contender for being my go-to ROM is currently Assonance 3.1.
Assonance is based on the I9000UGJK3 build, which is a Bell Canada Vibrant ROM. The nice thing about using this as a base instead of the usual American AT&T ROM is that it has network side caller name support (CNAM). Near as I can tell, only Canadian wireless carriers provide caller name as a part of the caller ID (CLID) sent to a mobile device. From my limited knowledge of how old school Canadian phone networks are configured vs. American ones, one of the few big differences is how CLID is done (hint: Canada handles it in a much more sane manner). It does not include the Rogers APN settings by default, but I listed those earlier here. Alternatively, you can use APN Backup & Restore from the Market to restore the APN settings linked in this forum thread.
One interesting tidbit about this ROM is it features the SetiroN kernel. Due to a bug with versions of the SetiroN kernel before 1.4, there are issues when upgrading from a 1.3 kernel to a 1.4+ kernel. However, the one in this ROM is version 1.4.3, so upgrading to the latest 1.5.x kernels should prove easy (I’m personally waiting for version 1.5.2 before proving this hypothesis, mostly due to laziness).
So I recommend anyone with an interest to give this ROM a try.