There are mainly four mobile service provider in Malaysia:
Celcom, DiGi, Maxis, U Mobile
You may check the coverage on the map for the location that you want to visit in Malaysia. (Service provided by OpenSignal)
Most of the rural areas Celcom is the best. For example Celcom has the best coverage for Langkawi. For Kuala Lumpur, almost all of them are same and usable.
My duration of my Journey was only one week. Based on my experience 2 GB was going to be enough for web browsing, 2-3 hours internet voice call and for Google Maps. As you guess Google Maps is the main tool for most travelers, since it has the integration with Uber and Grab.
2 GB data is 10 MR and including the fee for sim card it becomes 25 MR, which is reasonable for a one week vacation. Below is the alternative plans if you wish.