Trans guy here. I haven't had to bind in a while (top surgery), but I wore binders from gc2b for years. I always found them pretty comfortable (as comfortable as a binder is going to get, anyway), and liked that they came in a bunch of different colors, including multiple skin shades. It's also trans owned, if that's important to you.

In terms of what to look for:

• It's really worth it to get a binder from a reputable brand. I wore a cheap Amazon binder for a few months and it was painful, I really don't recommend it.
• Shape can matter for comfort. I preferred a half tank style because I wanted as little extra fabric as possible (I'm a sweaty guy), but a full tank style can be less dysphoric because it looks less like wearing a bra. Same with racerback or full back styles.
• It's useful to have a few different colors. White and nude are both useful when trying to hide the binder under certain types of shirts, black or colors will hide their age better. Shape can also matter here - do you wear crop tops? You'll want at least one half tank. Tank tops? A racerback will show less under those thin straps.
• A compression bra might be more comfortable when working out, even if it's less good for binding.

I don't know your friend, but if they're just getting one binder to try it out, I'd recommend a half tank in a nude color that best matches the skin tone on their chest. That's going to be the most versatile under the most clothing. If they like binding, they can pick up more binders once they know more of what they're looking for.

Putting on a binder for the first time was life changing for me. I nearly cried from how good it felt to look in a mirror and see a flat(ter) chest. Best wishes for your friend!!

P.S. You can use tape for binding, but you shouldn't wrap your chest up in tape. The safe way to do it is to use a couple strips to "pull" your chest tissue into a more comfortable shape. There's tutorials online for this. You have to use skin safe tape - the kind athletes use for muscle injuries is available at most drug stores. (This works best if your chest is relatively small – mine was too big for this.)