You are young, you have time, go for the experienced horse, even a part lease, to gain competition experience and learn on. Wait on the Greenie who needs to be taught until you are knowledgeable and confident enough to teach that Green horse how to jump, handle terrain and solid jumps and answer the questions asked by the course, a packer will help you learn these things. Also help you meet people and make contacts that can help you learn of the better Green offerings…that are never advertised.
From your other questions, it sounds like you also need to learn more about the things that make up a good Eventing prospect and, most important, make contacts with active competitors and trainers in your region who, down the road, can be of great help to you. The more you know, the less you need to depend on the opinions of others…who may or may not have much practical experience with enough horses to guide you.
Watch, watch, watch and watch some more, the more horses you watch going around, the more educated your eye will become. Doesn’t cost anything but gas and maybe lunch. Listen around the schooling rings too, learn who the better riders and trainers in your area are- hint, they may not be the flashiest or biggest winners. Just the ones that can help you learn the most.
Pedigree knowledge is fine and there are strong and differing opinions BUT you must first look at the horse in front of you. As you get a better eye, you can see some common physical things that translate to a good jump. IMO a good canter usually can be developed into a good jump and is a far better indicator then the trot so many get hung up on., IMO . Learn to pick that out in any breed, like an Appendix fur example.
When I was much younger, made some really bad, expensive mistakes and bought some really unsuitable horses I thought I could teach, cost more then just spending more on a better one that could teach me enough to teach a Greenie anything beyond WTC stop and steer,. Like to see more young people get some packer time and get more involved in the specifics of their chosen discipline (like jumping) as well as get aquainted with their local competitors and Pros who may do more then ride and teach, as in buy and sell in quantity.
As I got older and became better known in my horse community at the time, I actually bought my best two horses in the 50 yeas I owned, one Western, one Hunter 20 years apart, when somebody called me…I wasn’t really looking either time. And they were both drastically reduced in price, one was downright cheap.
Patience, knowledge and knowing many people tends to turn up more opportunities.