I personally would go for rabbits every time, but we love bunnies here, so I am biased - for Rabbits you need to make sure you have a large enough cage - even better if you can have a safe free run for them -
our rabbit used to live freely in our yard, once we realised foxes etc couldn't get in, so e had a good life, he had free use of a big yard & sussed out the cat flap PDQ & we akways knew it was winter when we cane down to find him sat in the kitchen - if you can't let them have a yard, then they need a safe run where they an be let out supervised for as long as possible every day.
They are sociable animals & best kept in same sex or neutered pairs, (never with guinea pigs) so you do need a big cage, house rabbits can be trained, but watch your wires, they love chewing wires & will destroy if they get the chance, they get on well with cats, ours did & because if this he was fine as an only - he actually thought he was a cat :)
You need to think about plants, they aren't known as farming pests for nothing, they really can decimate a garden, they will chew anything to bits & you'll be surprised how high they can get - mine even ate my chilli plants - 20 scotch bell peppers in one go & went back for seconds - so you need to be prepared for things like that & cleaning & making sure they don't have fly problems etc, but even with all that to content with, they are wonderful pets & we still miss ours very much
Lionheads are a good breed for kids, I researched a lot before getting ours & everything I read was true, he grew up to be a big soppy thing, loved been handled & never bit anyone & DD often woke to find he'd let himself in, climbed the stairs & would get up onto her bed to wake her - they are bright animals :)
I'll leave the guinea pigs to others, they are probably easier pets, as they dont seem to climb, but they just never did it for me,