[Scuttler]

Essentially DIN is a more secure fitting. It screws into the valve.

A-Clamps are more common but increasingly I have noticed more and more DIN.

If you want to use a 300bar cylinder then A-Clamp is not an option.

In the long run if you envisage Twinset diving/Technical diving then go straight for DIN as it's more cost effective as you wont have to change first stages at a later date.

If all you'll ever do is holiday diving and the odd bimble (which I presume is what you do as you have a wetsuit but no drysuit???) then can't see anything majorly wrong with A-Clamp. IIRC there is little or no difference in pricing for the First stages but 300bar cylinders are more expensive and a lot heavier.

Just my 2p worth.