I completely agree with masiman. If your rides are short, occasional rides get the instep. If not, definitely go for the Chariots.
I bought a Schwinn (Target, made by Pacific Cycles which also manufactures the InStep) for my son but after a month of use I returned it and bought a Chariot Cougar2 (two kid version) after much deliberation between the Burley and Chariot. For me, Schwinn may not have been that bad if my son was older (he was 13 months old at that time), but he kept slipping forward in his seat as the strap adjustment wasn't really that well thought of on the Schwinn.
Chariot added fenders to their Cougar line up for 2009 (previously optional), so if you can find a 2008 model in REI you may get one at reduced price. Also, REI puts a 20% discount on the Chariots from time to time. The only bad thing about Chariot is, you need to buy the cycling conversion kit separately. They also have excellent jogging and stroller kits as well.
Ihsan