I haven't flown with either seat, so I can't tell you, but I've flown a ton with my daughter alone, so I do know about getting us on board.
First, once you're on they generally don't let kids back off. I would put Piper in a seat in our row or across the aisle first, then I'd install her seat. After the seat was installed I'd get her in it (she didn't need to be buckled, but she had to sit or stand in it, or in my seat) and then I'd stow our bags. I don't normally check luggage, so I'd have our roller bag and our carryons with us.
Now that Piper is older what she has decided on her own to do is to curl up under the seat in front of us. It's a bit of a game to her. Maybe you could suggest that?
Also, people want to board quickly, but they do understand that kids add to the fun. If a passenger offers to help, accept. If you're worry about getting the carseat and your stuff, then check whatever you don't want to take on board. If you have a backpack on then you can leave it on your back while you install the seat. Send the toddler toward the back of the plane (no exit, so they can't get off the plane, they're there somewhere).
Southwest will often board families after group A.
Don't go for a bulkhead seat.
Wendy