I live in Sarawak. Miri, to be precise and I kinda agree with Paladin up there ^ (I’m guessing you work on Toisa Paladin?? – I’m in the SSB subsea team in Miri). I wouldn’t come here on holiday, although I find it a nice place to live and work. It is the main route to fly to Mulu, however, which is worthwhile to go see some huge caves and loads of bats. And bugs which live on bat poo. And lots and lots of bat poo.
Anyway, nowt to see in Brunei. Pretty much avoid. Used to live there too but it’s really culturally bereft and not much going on tourist wise. The empire hotel can be nice as it’s an impressive resort but it’s hardly buzzing. And there’s a no alcohol law so not much in the way of partying.
Stick to Sabah, base yourself in Kota Kinabalu. Go diving offshore KK or head over to the other side of Sabah to Tawau, Sipadan etc. Very nice, even if you aren’t a diver. Even snorkling round there is nice.
Climb Mt Kinabalu. Stunning views and worth the hike.
Go see some small elephants and orangutans if that’s your bag. Also there’s a turtle hatching beach up there too which I sent my mum too but never been yet.
Dont expect it to be a lush jungle wilderness.. It’s pretty much all gone now except the far interior of the island. All replaced with palm oil plantations and the like. Rather sad to say the least. Likewise some of the near shore reefs are in a bad state but Sipadan is very impressive.
HTH