I use a breastcollar on my western saddle, mainly for riding trails. Somehow no matter what I plan I end up crossing gullies and going up and down giant hills.
It's really a no-name nylon breastcollar, kind of matches my cordura saddle, and has thick felt padding all over the back, so no fear of rubs. Plus, as my dad says, the horse looks fully dressed with it on.
I don't *need* it for general riding or to keep the saddle from slipping on the flat, but it just kind of lives on the western saddle.
If I jumped more maybe I would invest in an English breastplate. Those I could picture rubbing (leather on coat) unless they are lined with fleece or something, and that runs up the price tag pretty quick.