A word of warning to all: avoid the Padang Besar border with Malaysia. I was turned down for no good, sound reason (made up inconsistent requirements about cash currency and paper-printed hotel bookings). The officer was rude and unreasonable and I was given an expulsion slip! Went to the Sadao border and granted entry. However, I can confirm that an instant u-turn re-entry is impossible at both. The friendly Sadao officer who let me in after one night in Malaysia recommended minimum 3 nights in Malaysia and said Laos is still the best option. That being said, two older guys I met in Malaysia (with perhaps more back-to-back visas) were denied entry at Sadao as well based on an entry cancellation stamp stamped at Padang Besar. Avoid PB at all costs, they are extremely unfriendly towards white / western foreigners.