Siem Reap, Battambang and Phnom Penh: what order?

The cheapest sensible order is Phnom Penh → Battambang → Siem Reap — €13 of transport and 0.6 days spent moving.

Phnom Penh → Battambang → Siem Reap

• Phnom Penh → Battambang Bus 4h €7
• Battambang → Siem Reap Minivan 2h 17m €6

You fly into PNH and home from SAI — an open-jaw ticket, usually cheaper than doubling back.