I agree with getting a vet check on either one of them. I would never buy a horse without one. I also suggest x-rays on at least the front feet. Consulting with your trainer is a good idea and if you can take her with you to check them out, watch you ride and ride them gerself, that could be beneficial as well. Good luck.
I would say the chestnut, if your'e not looking for a confidence builder and would like a bit of a challenge, the grey is 10 and probably has reached its prime time in life, so you wouldn't really be able to progress with it as much, the chestnut is young so has potential to work with.
Either could be fun depends which you prefer.
If you don't feel inclined to one of them perhaps look at a few more first.
I think they both sound like something you would have fun with...my only thing is the chestnut kind of hangs her knees a bit...not ideal for the jumpers...but...if she is powerful enough with her hind that could make up for her front end a bit...I can't comment on the grey's knees cause of the pic...but he seems to have a decent hind end...but I like the experience the chestnut has since that is what you want to do with her....good luck deciding! How exciting!
I like the chestnut from your description (Will go back to look at the knees once I have posted) - but if they arent too bad it may be just that one jump - get your trainer to have a look at the vids.... see what she thinks from there