A.,
I bought the sit and stand/Joovy caboose and actually found it on Craigs List, saving about $75! This way I figured if it worked, *great*; if it was a flop, I'd just resell it there and break even.
I considered the Phil and Ted's but didn't get it for several reasons: first, the older child is supposed to go in back. While everyone and their brother assured me the older kid loved this placement, I wasn't convinced my 3 year old would like hearing everyone see/notice her baby brother and make a big deal out of him without giving her props :) Additionally, she's a busybody (as most toddlers are) and I thought the obstructed view would not be appealing. I was also worried about the weight limit (she was pretty close as she's tall) and wondered the same as you: for how much longer would she even want to be in a stroller?
I recommend going to Babies 'R Us with your toddler and trying them all out. I had fallen in love with the newest Graco double stroller, but opted out of it when I realized how heavy it was (try lifting them up when collapsed to *trunk level*) and how much room it would take up in my trunk! However, I can understand how lots of people go for it as it's a luxury stroller for sure!!
I absolutely love my Joovy, as my toddler has totally bought into it. She loves that she faces me when sitting and can stand if she wants to while we stroll along. I love that it's easy in/easy out for her, since sometimes she just wants to run alongside me rather than be pushed. In the end, that was the best option for us.
Good luck in your search :)
L.
p.s. I also would suggest going to the Babies 'R Us site, once you've narrowed down your selection, and reading the reviews there. Those editorials from other moms are what made me opt for the Joovy over the Baby Trend version of the sit and stand.