I prefer sticky! To be honest it doesnt matter too much as long as it FITS. Please dont be tempted to use any old thing just because its for backing. Ive seen some horrendous saddles chucked on youngsters before now and people wonder why they dont have an easy time of it!
I think the Wintec is a good bet, easy to sell on later if needs be and not to huge a purchase price for you.
I used a Treefree Dartmoor for backing mine (esp as wanted to ride bith treed and treeless) and then got a Thorowgood XW cob (shes a Haffie).
The Thorowgood is adjustable and both saddles would be easy to resell but I cant sell either as she still loves them bith 2 years later. The Thorowgood 4th breeching girth strap is very good for a feeling of security!! and adjustable fish helps with changing shape. It cost just over £200 new whereas the gorgeous Treefree was £400 second hand (with all its bits and bobs).
I recently backed my boy, and I used a Cashell Pad. Which is much like a thick neoprene type material soft saddle, with a seat like shape, which literally fits on like a numnah but has stirrups and a girth attached to it.
I found this excellent as it is so light, soft, non-invasive and fits anything as there is no fixed shape to it.
They cost about £100, and are also great for use at the beach as they can get wet with no damage incurred.
I then had a saddle fitted to him after I have ridden him for about 3 weeks in the Cashell pad. I bought a Wintec as he is still growing and they are not as heavy as leather or treeless.
I have always used my exercise racing saddle for backing, with a gel pad & a poly pad underneath & usually a chamois leather against their coat, especially if they are still quite a baby ish shape.
The racing saddle is SO much comfier for leaning over & no big cantle to get your leg over!
My instructor uses an old wintect pro jumping saddle to back youngsters. He says that he likes the flat seat as it is easy to eject in case of difficulties. I would imagine it's a similar principle to the racing saddle.
I used a Wintec cob for my young Arab when I backed him - on the basis that it was light, fitted well, and was relatively cheap so I wouldn't be heart-broken if he damaged it or when he grew out of it (which he did after 18 months).
As some posters have said, it is imperative that the saddle fits and is comfy for the HORSE. It is also essential to have the fit checked at least six monthly, preferably more often.
I backed Axel with a Wintec Isabel, and he still has the same saddle now 3 years later!
I found I wanted the opposite I wanted to have something with a nice deep seat to keep me on lol!