Which RAMs should I take: 168 Pins or 184 Pin DDR ?

I currently have a motherboard which can hold
168 Pin RAMs as well as 184 Pin DDRs. The motherboard offers 200 + 266 FrontSideSpeeed.

I am now have to decide which RAMs I should take.

Are 184 Pin DDRs faster than 168 PINs ?

How much faster (without overclocking) ? 20% ?

Which RAM type has more future ?

Possibly I change in a couple of month/years to another, newer motherboard.
Which type of RAM is more likely to fit into the new (currently unknown) motherboard?

Ok, I know, for exact statements you need the exact specifications.
But I don't know which motherboard I will buy in the future.

I only would appreciate to have rules of thumb.

Peter