Well, our elder son is off to jump on his national pony club team at the British Open at the NEC this week and he wouldn't have had a chance to have a fantastic opportunity like that without the pony club.
I would recommend that you research carefully which branch to join as some are more active than others and some tend to focus more on certain disciplines, although all will be catered to at some level. There are lots of team and individual things you can aim for, and lots of prestigious finals to get to.
You can go to one rally before you join as a taster which is worth doing imo.
You can get a fairly good idea from the website too - some run shows most months and rallies most weeks while others run next to nothing in comparison - bigger ones tend to run more in my experiences.
Hell yeah! Pony club is fantastic! You meet loads of people your age who live in the same area as you who like horses and learn to ride at the same time!
(PS: I am a devout pony club fan... I want to go to camp until I am 26!)
I can tell a PC rider at local shows because they usually dress smartly, and don't do bling! Most PCs prefer members to wear tweed when representing the branch at competitions, and at rallies they prefer plain numnahs and traditional tack (ie no diamante browbands!), so this tends to become a habit, although some are less strict on what to wear.
On the plus side there are some great opportunities to enter team comps and it is lovely to be part of a team where everyone is cheering for you.
On the down side there are always internal politics and it is harder joining as a teenager because you won't know all the ins and outs. some branches are really friendly and will make you feel welcome, others it takes a bit more effort to make friends.
You will be encouraged to join your nearest branch, although if you live between two then go for the one that is most active in the discipline you like best, which sounds like show jumping.
Look on the pc website and see if you can tell which branches are nearest you, then ask on here for the low-down. I know one of the Norfolk branches, but not very well so can't really say which would be best.
Yeah, agree with above re being careful which pony club you join. I'd say though it is useful, with cheap training etc, it doesn't suit everyone, kinda depends on your attitude to it!