If you are trying to get the achievements that are for getting all the golden hats and spoilers, then Jon is your best bet. (idk about time trails because I didn't feel like using that method).
Odie is still useful for getting the puzzle piece's achievement because of his synergy with the hat that lets players spring higher.

Odie may be faster than Jon, but the game became much more consistent once I switched to Jon.

Jon is really good at staying in 1st once you get in first because of setting pie landmines for the drivers behind you. With 3-6 pies at a time, you can create walls of obstacles to cover the road on turns and some areas were the road is only 2 carts wide. Placing them right before, on, or right after boosts is also powerful because the CPU's will end up taking the hit and fall behind by trying to use the boost, or not take the hit and also not catch up because they didn't get to use the boost.

Also Jon being able to hold 3-6 pies makes moving from 3rd to 2nd or 2nd to 1st much more often and consistent than Odie because of those red seeking pies. Jon can burn out the power ups of CPU's trying to defend against his pies, which one (or some) will sooner than later land.

Trying to rely on Odie's speed sounds good, but Jon just has better tactics than relying on speed in this game where the CPU's play "dirty" anyways. There have been many times I would have won as Odie but a CPU's power up or them ramming into me would cost the win (this is less often with Jon, as he would be far ahead while the CPU's are fighting each other and tripping over the minefield he left behind)

All in all, I would say Odie is great for collecting puzzle pieces with his extra jump height hat (which is why I was using him a lot at the start), but Jon's pies beat Odie's boosts (in my opinion at least). That's why I'd recommend using Jon over Odie.

hope this helps because switching to Jon certainly helped me.