As a regular visitor to both countries - I would recommend going to Sabah - Kota Kinabalu. These are my reasons:
1. Definitely very unspoilt and clean environment - good clean air, nice people and good food (especially the seafood).
2. Very safe for water sports (as many sea areas are relatively calm) - there are many hotels that offers water sports like jet ski, parasailing, fishing etc.
3. A must visit to Mt Kinabalu - to see the only tropical rainforest in Asia.
4. No language barrier - most people speaks cantonese.
Try..you will not regret. Also, try to stay at the Tanjung Aru Resort - it is very beautiful.