I love my cheap, synthetic, Thorowgood saddle for trail riding. It's an english saddle, but the synthetic material makes it nice and sticky. Very deep seat and I can get it wet without worrying about it.
I don't know of a good comfortable A/P but I have an extremely comfortable dressage saddle, a Wintec Isabell. Definitely one of the most comfortable saddles I've ever ridden in...and since it's synthetic it could easily stand up to mud, water, and dirt from the trail. Every now and then you can find one used for a great deal..I found mine for $400 in pretty nice condition, only some minor wear.
And I think it's worth noting, if you're at all interested in a western saddle, the absolute most comfortable saddle this butt has ever met (and it's met plenty of fancy expensive trail saddles) is an Abetta Brushpopper, only $406-453 (depending on seat size) at Abetta Brushpopper Trail Saddle. This saddle is INCREDIBLE. It's basically an Abetta Pathfinder but with a cloud for a seat. It has a HUGE layer of memory foam over the entire seat and it feels like heaven. Once you sit in this saddle, you will honestly never want to leave, hahaha
It also has nice padded trail stirrups for even more comfort.
And since it's cordura it's very lightweight and safe to get it wet.
I adore it.
They also make a really similar saddle in an endurance style without a horn. http://www.buytack.com/products/saddles/act/20554.htm
I use A/P Collegiate Dignitary for trail riding. It's really deep even for the the A/P saddle, but also can be used for light jumping. If you need a saddle ONLY for the trails, dressage could be even better idea. As for stock saddle - it's great but (in my area) hard to find a good one (I never order saddles on Internet).
I use a wintec AP for my everything saddle including trail riding. I like not having to worry about getting it wet or dirty. Dressage saddles are a great idea too, the longer length flap can be more comfortable on longer rides and the deeper seat will keep her secure just in case.
I have a Crates Saddle Co. saddle.. that Ive been using for a long time, never had any soreness issues with it. It works great for all things trail, especially if your riding for hours It's 22 years old now, and it's still the best saddle I've ever had! XD