A lot of people knock the All Purpose saddle, calling it a “no purpose” saddle that makes too many trade offs to be suitable for either dressage or jumping.
In some cases, that’s true. But you shouldn’t cross the A/P saddle off your list. Depending on your goals and the design of the saddle, it might be your most comfortable choice in a saddle. I often ride in my A/P saddle because it allows me to be balanced on the flat (and ride with a slightly longer stirrup than my jumping saddle but a shorter length than my dressage saddle) but still hop over small jumps. I find it very comfortable for hacking because of the compromises. In fact many foxhunters also ride in A/P saddles because they offer a good solution for riding that spans both flat and fences.
However, many all purpose saddles are designed either with a dressage tendency, with straighter flaps, or a jumping emphasis, with a slightly more forward flap. Which one you choose depends on how you like to ride.
I grabbed a few saddles from our barn to show how the different designs compare. Freedom is modeling the saddles but they are not all mine so some of them don’t fit him quite right.
This is a classic All Purpose saddle with more of a jumping slant. I ride in it quite often because it's beautifully balanced, allowing me to flat in it and jump small fences. You can see that if you tried to really shorten your stirrups, your knee would go over the flap but the stirrup bars are far enough back that my leg drapes naturally with a longer stirrup. The seat is not too deep, but isn't flat. You can't tell from this view but it has no blocks or knee rolls. This is an Austrian saddle, so unfortunately not a brand you can find readily.
This is my Wintec Pro Jump saddle. It's considered a close contact saddle and it has a pretty forward flap (more than the Wintec close contact). You can see that the forward flap allows you to shorten your stirrups to give you a base of support over fences. The stirrup bars are still reasonably far back so this saddle allows you to keep your lower leg underneath you. The seat is quite flat which I prefer because sometimes over a fence you don't want to feel locked in. My knee comes pretty close to the edge of the flap but I use it for foxhunting where I like to ride a bit long.
This is a Wintec A/P saddle with a tendency toward dressage. Compared to the Pro Jump you can see that the flaps are much straighter, the seat is deeper and it has a big knee roll and block. Look closer and you'll see that the stirrup bars are closer to the front of the saddle. Although this saddle is an 18" saddle, compared to the Pro Jump, which is a 17.5" saddle, the knee blocks and the seat make it ride smaller. This isn't my saddle so I've never ridden in it but I've observed that it puts the owner in a slight chair seat. That doesn't surprise me because the saddle supports a leg forward position.
This is a Stubben dressage saddle. It has a lot of the same characteristics as the Wintec A/P -- straight flaps, deeper seat and big knee rolls. However, the stirrup bars are further back which allows you to open your hip angle and keep your legs under you. In this case the position of the knee blocks helps keep your knee down with a more vertical leg position.
Just to show the full spectrum of saddle flap designs, here's a Wintec cross country saddle. This saddle has an extra forward flap and a flat seat. You can see that the stirrup bars are place forward (there's a lot of seat behind them) because when riding xc in a half seat, jumping drop fences, etc., it's preferable to be a bit behind the motion. I love this saddle for jumping but it puts me in a chair seat on the flat because it's hard to keep my legs under me. However, it's one of the few saddles that lets me put my stirrups up without sending my knee over the flap!
I didn’t mean this to be a Wintec comparison but that’s what was at the barn on the day I was taking photos!
In conclusion, A/P saddles can be a good choice for you and your horse if you don’t want to jump larger fences and you don’t need to have a really vertical leg position.