Hi,
The 3500 is better for a core than the 2910al as it supports more features, Provided you buy the premium pack. I would go for the newer 3800's though as they do not need this and have 10gb uplink ports built into it and support routing/vrrp etc so you can have a core that has resilient. You can stack a 3800 also so your core can start to do away with redundant links being blocked by spanning tree. Another good core would be the 5500-hi box which you can link together with the 2 10gb ports over irf and cheap copper sfp cables.
If you only have a flat layer 2 network and you want to switch between say low end 2500's/2600s then a 2910 would work but its layer 3 and vrrp support is questionably poor.
J
