Visas on Arrival are very efficient but you do potentially get bogged down waiting for the visa once you land at the airport. We did the VOA and were slow to get off the plane so I think we waited about 30-45mins at HAN which wasn't too bad. We may have lucked out though because we seemed to get our passports back before others waiting.

I wouldn't necessarily discount getting a visa before you leave if you have a consulate or embassy in the town where you live and it's convenient for you to drop your passport off.