As the topic says, which server would you prefer as a reseller? Which would increase your confidence resp. which do you think would be better marketable towards your own clients?

We've got a stack of both and used to only use Intel CPU's. At some point we put together a dual Opteron server to test out and since then we haven't put another dual Xeon server online (unless for a client dedicated server). The performance difference of the Opteron is noticable over the Xeon.

As for being marketable, I'm not sure either stand out there. It doesn't tend to bother me anyway though as we choose server hardware for the performance, not the bragging rights.

Same here, I use to have all Intel CPU's and have now switched to dual core Opterons. The Opterons seem to run so much faster and cooler than a dual xeon. There really seems to be a large difference when you host a lot of mysql sites; that's when the opeterons appear to be the clear winner.