This is tough to condense into a simple answer, particularly not knowing too much about your background or what you’re going for. I speak from the perspective of an American-Malaysian of Chinese ancestry who spent most of my summers growing up in Malaysia. Also we live in the US currently but have been plotting a move to Asia for many years now and currently still agonizing over choosing between Malaysia and Taiwan (if you’ve read my posts on here then you’ll realize we are about 90% set on Taiwan). So I’m familiar with the two countries and cities being compared, but I have never lived in either one, fyi
The biggest difference to me is that KL will feel much more Anglo-centric. There will be little issue with day-to-day tasks speaking purely English. You will need some Malay in certain instances, so you’ll end up picking up some necessary skills there, but by and large English will suffice. Also note that the most common Chinese spoken in KL will be Cantonese. If you opt for a Chinese public school for your kids then they will get to keep up their Mandarin some.
As mentioned by others already, the built environment will feel quite different too. KL is sprawling and very auto-centric. The transit system isn’t that bad (remember I’m an American) but it’s certainly not anywhere on Taipei’s level. There are many decently walkable neighborhoods, but overall walkable connectivity is low and doesn’t come close to Taipei and vicinity. Also, the lush, green nature doesn’t compare to what can be found in and around Taipei either. You can find some nice nature 1-2 hours outside the city (depending on traffic). There are some nice suburbs of KL, and these are even more auto-centric and very American in feel.
Weather sucks (imo) year-round in KL. No reprieve from the heat like Taipei gets at least. Think of Taipei summer basically all year round. I like KL’s location for consistently cheap airfares and easy access, although hopefully you’d be getting perks so the low prices won’t matter as much for you.
I think you’d find a greater expat scene in KL, at least as far as Anglos go. Definitely more diversity with Malays and Indians being such large communities along with the Chinese. I think food is better although I love Taiwanese food also, so it’s a marginal difference. Costs are gonna be approx the same as well. I think your money will go a bit farther in KL in terms of real estate (size/quality) but that will probably depend a lot on your exact location. The big x-factor would be whether or not you need to get a car. Can’t speak to your industry necessarily, but local professionals and college grad wages are very low, just like in Taiwan.
Good luck to you! My cousin had been trying to land a job in Singapore for several years to no avail…finally she took an offer in JB since that company also has a Singapore presence. She will hope to eventually make her way across the border.