I have had the opportunity (misfortune) this year to earn Platinum status on both Delta and Continental with BIS miles (125k on DL and 75k on CO). This has allowed me to get a very good feel for both airlines.
Both Delta and Continental have excellent hard product. CO has the edge on aircraft 'feel', but DL flies larger planes on my routes.
Staff and Crew have been great for both.
It is hard to argue with 'meals at mealtime' for CO. I end up grabbing food before or after flights with DL.
DL has better schedules for my routes. DL also allows me to book O/W trips without forcing me into H or Y fares.
CO routing is a little better with IAH as a HUB.
the ATL hub for DL makes the red-eye from the west coast feasible (more sleep time).
DL doesn't charge me for SDC standby.
DL has a cheaper change fee.
Upgrades on DL were better as a Gold than CO as a platinum.
I only plan of flying enough next year to get top status on 1 airline. I haven't decided yet which loyalty program I will stay with, but the cheaper change fees, free SDC, and more versatile routings (with better upgrade possibilities) of DL is pretty compelling.