I spent 4 of my 5 years at UAL commuting to reserve (my choice) and realize only now that its time I'll never get back. I was furloughed from UAL in 2003 and came to JB and am now a bus captain living in base. I'll likely make much more money over the next 5 years at JB, although, I'm likely giving up greater career earnings at UAL. Its taken me a long time to learn - and you have to realize this for yourself - you can always make money, but, you can't make time. I can't emphasize this concept enough - this is what compelled me to resign from UAL last week to stay at JB. If I lived in ORD,DEN, DCA, etc., etc., I would have gone back to UAL in 2005 and never looked back.
As stated in previous posts, pick the airline that promises the best quality of life - each have unique advantages/disadvantages and I believe both will be viable over the short/intermediate term. United will be negatively impacted by age 65 to a much greater extent and perhaps has a greater risk of merger or acquisition as well as labor issues coming to a head. Jetblue offers less career diversity at present (versus UAL) and has taken on a lot of debt which may or may not yield returns in the next 5 or 10 years.
Best of luck in your decision-making!