PSN marksman Rifles

have kind of a dumb question as I'm new to The Division. I recently got a 256 First Wave M1A & have it fully moded at 253,326 DPS with 42.4 K damage but have been using my 229 Military Scar-H 348,260 DPS with 40K DMG with should I use?

Look at the damage per bullet, it will give a better idea of which one to use.  To achieve the listed DPS, you have to be hitting every shot and for snipers I think they need to be headshots or crits to get those numbers you list.  When you start missing DPS starts dropping.  However, the base weapon damage will always be the same whether you hit 1 of 3 shots or 3 of 3.  You also need to take into consideration weapon talents, whether or not they're active (lit up and not grayed out) and what's needed to activate them.

TLR - pick the sniper with the higher base weapon damage, possibly consider the weapon talents.