Both routes are legitimate. They suit different travellers, and the difference matters most on the day you land.
E-visa
Fully online, no queue on arrival, works at airports as well as land and sea gates. You know the outcome before you board, which is the main reason most travellers now prefer it.
Visa on arrival
Requires an approval letter arranged in advance, then a stamping counter at the airport on landing. It is airport-only, and the counter queue can be long after a wave of arrivals.
Cost
Visa on arrival splits the cost between a service fee and a stamping fee paid in cash at the airport. Budget for both, in the accepted currency.
Which to choose
For a straightforward flight into a major airport with time to prepare, the e-visa is simpler and more predictable. Visa on arrival remains useful for very short notice cases where an approval letter can be arranged faster than an e-visa.