As a solo girl on my way back from Bali to Hong Kong, I stayed overnight in Singapore and booked at the Inn Crowd. It's clean, the staff are genuinely friendly, and the place is bustling without being TOO bustling, which gets on my nerves. Large coed dorms and some private rooms. Reasonable price. Bar downstairs. Colorful paint. It's like the lego house of clean hostels.
The Inn Crowds (Dunlop and Campbell street locations) are within a block or two of one another in the Indian Quarter of Singapore. Great shopping and food, very close to the MRT, safe, convenient, etc. I think the Campbell even has a cat!
The InnCrowd Backpackers Hostel, Singapore