Hey Tana, Book hotel with OYO or MMT near Mall road of Gangtok ( best location). During North Sikkim tour everything will be included in the package so you have no need to select hotel and location. Happy travelling!!!!!
We stayed in hotel coral inn in gangtok and hotel takura in pelling. both were decent budget properties. Lachen and lachung dont have much options...majorly homestays that are very basic. Happy travelling!!