A Strider bike!! Our daughter went from pedaling a Fisher Price trike at 18 mo. to a strider at 2 1/2 and now she just got a 12" big girl bike for Christmas (she will be 4 this month) and literally within 1 hour outside, she could ride the new bike without training wheels. Less than a month later she was cruising all over the neighborhood and starting and stopping by herself.
We went backwards with her older brother and started him on a Strider but then he got a trike from Grandma and that became his go to bike. When he was 4 we got him a bigger bike (one size up from 12") and at 5 1/2 he is still using training wheels with no sign of giving them up.
My recommendation is definitely a Strider bike and then go straight to a 12" without training wheels. If you go with a balance bike, we LOVE our Strider brand.