In recent years, mobile signal in the Everest region has improved dramatically. You can now get 4G coverage in many spots along the trail, even as you approach the Mount Everest summit region.
Ncell generally offers better 4G speeds in Namche Bazaar and Lukla. It is the preferred choice for trekkers wanting to upload photos of their Everest Base Camp journey quickly.
Nepal Telecom (NTC) often has better coverage in the more remote valleys. Many Mount Everest expedition leaders carry an NTC sim as a backup for emergency communication.
Once you pass Gorakshep and reach Everest Base Camp, the signal becomes very spotty. Most people switch to the 'Everest Link' Wi-Fi for reliable connectivity at the foot of the Mount Everest summit.
Buy both SIM cards if you need constant access. They are cheap in Kathmandu and provide a vital link to the world during your Everest trekking adventure.