NTC, NCELL and Smart cell are major three telecom in nepal. Your question is not so clear whether you are asking for internet to use on mobile or computer but if you are talking about mobile the speed of internet depends upon the mode of data you use. 4G service has recently launched by NTC and NCELL. It is the fastest network but still it is not available in all over the country. NTC has error free server and is cheaper and faster than others.