A little more info on you and your ski crew's ability / level may help.
The tracking on the new one is surely better, but if you are 15-22 off skiers at 30-32 mph on a public lake, the tracking on the new one may not be as noticeable than if you start at -28 or -32 on the private lake and shorten from there.... (I'm really not qualified to say if -28 is the cutoff point, but I'd argue the logic applies).
I think the "21+ most noticeable items are inside / driver stuff. Bigger screen with more info easier to get to (radio, seat heat, etc), nice driver cubby spot for sunglasses and phones, awesome engine box, rear cupholders not on engine box (water bottles won't get hot), and lighter rear seats (if you are getting those) are some things I noticed.
Having said that 14-20 is still a great great great boat and will be for a long time.
Either choice is good, main factor may be what you want to spend and if you can find a 14-20 at a price you like with the options / colors you like.