Which telco has the best coverage for balik kampung to the east coast?

Coverage on the east coast really depends on your exact kampung, so general advice only goes so far. In my area near Kuantan, Maxis is actually the best, but my cousin in the Terengganu interior swears by Celcom. My tip: before Raya, check the coverage map on each telco's website by keying in your kampung postcode, they show data coverage by area. Also, the LPT2 highway now has much better coverage than a few years ago. If you're only going back a few times a year, just grab a prepaid backup SIM of the opposite network for RM10, cheaper than switching your whole plan. Two SIMs solved my problem completely.

I'm from Terengganu and drive back monthly, so I've tested them all. Honestly Celcom (now CelcomDigi) has been the most reliable for the east coast interior and kampung areas, their rural coverage historically is the strongest. Maxis is decent on the main highways but drops in the deep interior. What I do now: my primary is CelcomDigi and I keep a cheap prepaid Maxis Hotlink as backup for when one dies. With the CelcomDigi merger the network is still settling so coverage can vary by exact kampung. Best is to ask relatives in your specific area which bar shows full, coverage is very location-specific back home.