I have experience going to the Malaysia side, not Kalimantan. Have been to Kuching, serian, Miri, lawas, Tenom, Kota kinabalu, Sipitang etc. KK is my favorite for a couple reasons. It’s a nice city with many restaurants to choose from , can walk to the pier/ ocean for sunsets and there is a durian night market open everyday, when it’s in season and many other fruits too. If you travel outside KK an hour or 2, towards mount kinabalu or to Sipitang during fruit season you will be in for a real treat. Kalimantan is more off the beaten path, and my experience harder to get to, unless you are already in Indonesia. There are no direct flights from borneo Malaysia to Kalimantan. It’s seem the Malaysian side is a bit more open to tourism.