mylar varies in quality. some are low to mid 80% reflectivity, some are closer to 90%. Poly film, often called panda film, is 90% ish too. A good white paint with highest RBG hex (closest to FF:FF:FF you can find - some have a color reflectivity index, which is measured in percents of light reflection - the better spec to look at if available, but the closer to FF:FF:FF and flat matte would be the best, too) and flat matte will also be roughly 90% reflective or more. there's another white film (i remmebered - "Panda Film") i'm forgetting the name of... i believe it's a percent or 2 better but not worth the cost difference. if ever choosing something instead of a tent, any and all of these options are perfectly fine. Paint probably lasts the longest. Mylar layers are glued together and will separate eventually from the canvas etc.. the films are easy to puncture... all sorts of pros/cons to each.
It really doesn't matter which reflective material is in use, because you won't see a difference due to this factor. I think white look better, lol. you might see 5-10 umol/s more at any one spot when comparing them.. which is just as likely user-error in taking the measurement, lol.
matte is generally better than shiny. you don't want a mirror-like surface. This is why 'diamond-stamped' (a pattern of some sort) mylar is better than smooth mylar. If you use paint, flat matte white is the way to go. Poly film has that shiny quality but still works just as well as the other options. it still difuses the light well (spreads it all about)
tent quality -- thickness of poles (weight capacity) and the thickness of canvas are the 2 primary things you want to focus on. that is what makes a quality tent that will last longer than others and warrant any sort of premium pricing. Easy access is usually guaranteed with 3 walls that zip open, but not all tents do that.
i'm not a fan of the "fancier" tents with a bunch of windows or too mnay ports etc.. just creates more potential for pinhole light leaks. A window for a tent? that is purely for the people that can't control their OCD, lol. Stop eye-fucking you rplants 2-4 hours per day, lol. I prefer to limit my plant's exposure to me and anything else foreign. I don't need to look in there 5 times per day. Not a fan of windows. I like simple, but often with the premium products you get more than the basics.