Lehns is a reliable choice for budgeteers. There's nothing memorable about the tired yellowish rooms, or indeed about much of the place, but you're not paying a lot, and it's in the heart of a leafy neighbourhood, a 10-minute walk away from Koror's main street.
Some rooms, especially rooms 24 and 25 (the cheaper ones), smell a bit musty, but they're serviceable. The pricier rooms are larger and come with a kitchenette, but are not significantly better. There's a laundromat next door. Credit cards are accepted but there's an additional 5% fee. Airport transfers are free if you stay three nights or more.