If space is tight, a pair of adjustable dumbbells in the 5 - 50 lb range will do more for you than bands alone, especially if you're doing compound movements like rows or presses. The others are right that they're efficient, but here's something worth considering: buy one set of adjustables and supplement with resistance bands rather than choosing between them. Bands are cheap, they don't take up space, and they're genuinely useful for warm-ups, finishers, and isolation work that dumbbells don't handle as well. You get the versatility of dumbbells for your main lifts without the "do I have the right weight" problem that fixed dumbbells create.
When you're shopping, check the adjustment mechanism carefully - some use a dial that can wear out, others use pins that take forever to swap. Weight increments matter too; if a set jumps from 10 to 15 lbs, you'll hit a frustrating gap in progression. Test the grip texture if you can; cheap ones get slippery when you sweat. Also, don't assume the total weight listed is what you're actually getting - some manufacturers measure each dumbbell separately, so a "50 lb set" might only give you 25 lbs per hand.
One practical hack: if your budget is genuinely tight, buy one adjustable dumbbell first rather than a pair. You can do most single-arm work, and honestly, unilateral training catches strength imbalances you wouldn't notice otherwise. Then add the second one or a set of bands once you've used it for a month and know you'll actually stick with it. No point dropping money on a full setup if it ends up gathering dust.