Pick the one up before you buy it. Glass catches the light in a way that nothing else on that shelf does, and if it's got any color in it, hold it up and see what it throws on the wall when the bulb's on. That's the whole decision right there. A clear glass base with nothing happening inside it is basically invisible until you light it, and a colored one becomes the thing that makes the whole side table.
Where this goes wrong is rooms that already have a lot going on. Put a glass lamp with a busy colored base next to a gallery wall and a patterned rug and now everyone's fighting for attention, nobody wins, and the room reads cluttered instead of layered. Glass also isn't the move if you've got toddlers barreling through the living room or a cat who treats every surface as a runway, because it chips, and a chipped lamp base looks sad in a way a dented wood one never does. Where it earns its spot is bedrooms, where you want something that catches the morning light without shouting, and living rooms with a sofa in a serious color, a deep green or a rust, where a clear or smoked glass base lets the furniture stay the star. It's also a genuinely good call for small apartments, because clear glass doesn't visually take up space the way an opaque base does, which matters a lot in a studio where every surface is doing double duty.
For scale, measure the table it's going on, not just the corner it'll sit in. A lamp base should run somewhere around a third of the table's height, and the whole lamp, shade included, wants to land close to eye level when you're seated nearby, not towering over everyone like it's got something to prove. The mistake people make constantly is buying the shade and base separately and ending up with proportions that look like a bobblehead. Get them together, or at least hold a shade up against the base before you commit. On quality, run your hand around the base. A well made glass lamp has weight to it, real heft when you pick it up, and the glass itself is thick enough that you can't feel the seam if it's got one. Cheap ones are thin, light as a water bottle, and the fitting where the cord meets the base rattles if you shake it gently. The good ones sit solid on the table and don't wobble when you set a coaster down next to them.
If I were starting from nothing, I'd go for a smoked amber base over clear. It's got warmth to it even unlit, and next to almost any color on a sofa it looks intentional rather than accidental.