RX100 Mk3 is usually cheaper than Mk4 (sometimes by a fair margin) and pretty much identical except it is missing 4K recording. If 4K is not a high priority item, I would get Mk3 over Mk4.
RX100 Mk2 is a marginal update over Mk1 and really a step down from Mk3 in many ways.
If you are looking for something small, then clearly RX10 is outside of the scope...
Last edited by stargold; Dec 20, 2015 at 12:06 pm
Reason: To clarify RX100