Yes, yes I do have opinions ;-D.
Or mostly observations that among the few dozen kids we know around learning-to-ride-bikes age, the ones who have done well have:
- been put on balance bikes (or 'gliders') first.
- have then had bikes which are proper bikes (ie properly scaled down adult bikes) without training wheels. They are generally higher end ones, but not many were bought new and most of them will be worth about the same once outgrown and resold.
Meanwhile most of the ones who have had training wheel equipped, cartoon character themed lumps of vaguely bike shaped pig iron are still riding them.
There are, of course confounding variables in play. The former group of kids are also largely the ones who see their parents riding places, who have been carried on bikes, who have been given the opportunity to ride most times they leave the house, not just every couple of weekends on an hours trip to the park.
Buying something now for use in the spring seems a bit risky given how fast kids that age stretch out. My #1 is big for age, but he went from the right size for 14" at 3yo to a 20" from the same manufacturer by 4 and a bit.
If you're saying that because you're somewhere that's likely to be under snow all winter, then I'd probably delay purchasing.
Otherwise, I would suggest buying a balance bike/'glider' now, and using it as much as possible - whenever you walk anywhere in your neighbourhood. I've seen a few people go down the route of taking pedals off a 14" bike, but a balance bike will be way, way lighter and they'll learn faster. They're also cheaper.
Buy a pedal bike that's the right size when they are ready to pedal.