For a pure flow trail I would prefer a hardtail with the tires and suspension a little firmer than usual. Everything else is what I ride on every trail: 27.5 wheels and whatever tires I have on my bike at the time, which are currently a maxxis minion dhf front and a wtb vigilante rear. If there are a fair number of jumps I’d prefer something more on the long, low, and slack side in terms of geometry. With my lack of confidence on jumps, especially those with steep takeoffs and landings, I prefer something that’s more stable midair and can deal with a botched landing with minimal fuss.
Really a flow trail can be ridden on any bike, as they are not usually very technically challenging. The difficulty comes primarily from jumps, and bike choice and setup are dependent on what you’re comfortable with.
If you’ve got an assortment of bikes to choose from then HoH’s advice is spot on. And, as also stated above, you can have loads of fun on any bike riding flow trails. Never hesitate to experiment by making (even minor) adjustments to suspension, tires, tire pressures, etc. to see what works best for you.