Framed shower doors use thinner glass held in a metal frame. They cost less, but the frame tracks collect soap scum and mildew, and the metal hides the tile you paid for.
Frameless enclosures use thick tempered glass held by a few hinges and clamps. They're easier to clean, make the bathroom look bigger, and work with almost any layout, including single doors, corner enclosures, and full glass walls around a tub and shower.
Because frameless glass is cut to your exact opening, measuring is everything. Walls and curbs are rarely perfectly square, so a good installer measures on site and has the glass made to those dimensions.
Hardware finish is where you get to personalize it. Matte black looks modern, brushed gold looks warm and upscale, and chrome is a classic. Choose one that matches your faucet and shower trim.