We were in the exact same boat with 2 boys 3 years apart and birthdays 4 days apart. After suffering through approximately 8 months of carrying the infant at the end of an outing so the 3 1/2 year old could ride in the stroller I bought the Joovy Ultralight and LOVE IT!
I saw one at the zoo and was overcome with extreme stroller envy at how easy to use it seemed to be.
My 3 year old is very active and usually only pooped out at the end of a zoo outing or a very long walk and the seat on the Joovy is great for him. He can rest for a bit then get up and explore more. He is not at all jealous that his baby brother has a different type of seat. Now, we are typically not out and about with the stroller when the 3 yr old would need to nap so if that is a typical scenario for you, you may want the double stroller.
Congratulations on number 2 :-)