Seamless is a pain in the butt and rarely looks good without retouching. Most people don't know how to roll it so there isn't an odd line at the transition from vertical to floor (99% of student work). And a lot of photographers either photograph it in too sharp focus so you see every defect or it just looks lousy in general.
White works if you put light on it so it goes to a highlight tone without detail but isn't burning out. Again, that takes some brain power to achieve. Black works too but it's pretty boring and hair lights reek of cheese.
Some people buy Muslin because it's cheaper than canvas but it always looks wrinkled and crummy.
Way better to get a painted canvas backdrop if you can afford it.
https://www.gravitybackdrops.com is a place I haven't used but it's representative of the type that's out there. There are really beautiful backdrops from big NYC places like Oliphant. You can rent them.
You might even make one yourself. I know of a fine art painter who makes backdrops for her photographer husband and friends. It's not impossible. That's basically who is making the rental backdrops. Ask around a theater department as well?
For $100 or so you can get a Denny Mfg painted background from B&H. I have an old one that folds up like an elephant's diaphragm, it goes about 6x8 feet and has a lighter and darker side. If you are careful with how far the subject is in front of the background (and aperture) you can make it look like a million bucks.
There's a reason most fashion studios build painted cycloramas for backgrounds ;-p