I've been to both Kuala Lumpur and Taipei, and the downside for them is the distance that the airports are from the city. For KL there's a fast train link into the city, but Taipei only has the buses chugging along.

That said, they've both got enough to keep you entertained for the better part of a day - in Taipei the night markets around town are well worth a visit, great food on offer. For KL I enjoyed Batu Caves, and there's the Petronas Towers to look at and you can go up Menara KL for getting a view of the city.

Neither are essentials though, for both Malaysia and Taiwan I've found the highlights to be out of the cities - but they're pleasant enough to spend your time in.