C.M.
I agree with the other posters
I would vote neither.
Children will sit up when they are ready.
3 months is too early. I think most babies are developmentally ready to sit no earlier than 5 months or so.
Until then, their bodies are not made to be seated.
Even once they are older it is unwise to force them to be in any one position.
Sitting in those chairs can cause spinal problems because their bodies are not ready for the stress of all that weight being compacted down on their spine and hips.