Both are racquet sports played on a small court with a net in the middle. That is roughly where the similarity ends, and choosing the wrong one first can cost you a few frustrating weeks.
How quickly you will have a real rally
Pickleball: the first session. The ball is slow, the paddle is short, and the court is small. Most people sustain a proper rally within ten minutes.
Badminton: the third or fourth session. The shuttle decelerates sharply and unpredictably, and judging where it will arrive is a skill nobody has on day one.
If your main worry is enjoying yourself immediately, pickleball wins clearly.
How hard the ceiling is
Badminton is the deeper game. It is the fastest racquet sport in the world, it demands real footwork, and there is essentially no limit to how good you can get. Players improve for decades.
Pickleball plateaus sooner for most people. That is not a criticism — it is why the social side is so strong — but if you want a sport that keeps beating you, badminton is it.
What each does to your body
Badminton is hard on knees and shoulders. The lunges are deep and the overhead action is repetitive, and a badminton player who does not warm up properly will meet a shoulder problem eventually.
Pickleball is gentler almost everywhere, which is why it has grown so fast among people over forty. The exception is the sudden forward dart to the kitchen, which is the commonest way pickleball players hurt themselves.
Playing alone
Both are usually doubles, so both are good for turning up without a team.
Pickleball has the social edge: the rotation between games is faster and people talk between points. Badminton doubles is more intense and less chatty while the rally is on.
The honest recommendation
Start with pickleball if you have not played a racquet sport before, if you want to enjoy the first session rather than the tenth, or if you are joining for the social side.
Start with badminton if you played anything racquet-based at school, if you want a sport that will still be challenging in five years, or if you want a proper cardio workout rather than a game that happens to involve moving.
Or do both. They are on the same flat tariff at KGB, the footwork transfers better than people expect, and plenty of members play both in the same week.