Ocean Kayak 12-Feet Malibu Two Tandem Sit-On-Top Recreational Kayak - we added seats (Ocean Kayak Comfort Tech Seat Back for Sit-On-Top Kayak)
Old Town 10-Feet 6-Inch Dirigo 106 Recreational Kayak
I like having the mix of both, but would favor the sit on top if I had to pick one.
The sit in is lighter (easier for one person to carry), and, therefore, faster in the water.
The sit on tops allow the kids to more easily jump in and out of the water - a BIG plus for us.
I like having this particular kayak in the mix. Although it is the heaviest, it has the most storage (nice for day trips), and allows the dog (or a small child) to tag along for the ride.
As it might help you make your decision-
We are beginners to kayaking, and have just been on lakes. Our children (10 and 13) can handle all of the kayaks we purchased. They both prefer the sit on top style.
We purchased 3 different paddles. Our favorite one is padded: Shoreline Kayak Paddle Rounded Blade 220 length.
The cart we purchased was: Malone Nomad Standard Universal Kayak Cart
I don't know that there are any cart options that make moving a kayak hassle free, but this one does the job. We liked it enough to purchase a second one.
Another helpful purchase:
SealLine Baja Dry Bag 20 (Yellow)
You can see size descriptions in other comments (VERY helpful). 20 was a perfect size for us as it can be made smaller. I carry phone, $$, snacks, med kit, napkins, dry clothes. No issues with it, and I like not worring about things getting wet.