It is an easy 90 minute drive from Jaipur to Amanbagh, but not easy to get from Amanbagh to Agra - not something I have ever tried. Normally, everyone goes to Agra from Delhi. However, driving from Amanbagh to Delhi once took me around 5 hours (not a great experience). If you could get to Agra from Amanbagh, then that would be great, but the only way I know is via private charter, taking off from Amanbagh air strip (approx 30 mins away from the resort). Pricey though.
As for Aman Delhi, I have posted my thoughts on this elsewhere - a search should find them. Not a great experience, but it should have improved since GM Henry Gray took over.