dear son has all 3. the exersaucer was a pass down item but we didnt let him play at all..
so far he loves his jumperoo and walker. he used to love his jumperoo more but now, walker. as for jumperoo, it would be better if an adult is there to supervise. i usually will sit beside and 'teach' dear son how to jump cos he tend to jump in a very tip-toe way.
as for walker, we try not to leave him alone in the walker, cos he will go around to take things. and i dont think is good to sit in walker and 'walk' so long time.
your baby is only 3mth+, i think better wait until she is at least 6mths old before placing her in walker. as for jumperoo, dear son started playing it when he was 5mths.. but must depends on individual babies, whether their neck is strong enough, 3mth+ is too early i think =)