Having just returned from 8 days in Kota Kinabalu in Sabah Borneo here are my thoughts & comparisons to Bali.
Kota Kinabalu - No hawkers!!!
Weather - same for both.
Bali - Way friendlier people, easier to have a chat with and even ask question. Magellan Sutera Harbour resort was fantastic but seemed to cater more for Asian guests and seafood lovers very few western style dishes or even M'lay type foods.
Taxi's - cheap in both but most could not speak English in KK. Money - no scamming changers in KK.
Clothing - KK found not much cheaper than in Australia. Not much on offer at the markets. Bali is a much better place to shop.
Food outside of the resort was always a taxi ride and you needed to know where to go rather than being able to walk down the road as in Bali and just drop in anywhere.
At the end of the day for me Bali win's out hands down but if your interested do lots of research as most attractions are spread out across Borneo not at Kota Kinabalu and perhaps spend a couple of days at each area.
Booked for Bali July/Aug 2007
Fernandez