I've been active for over four years, and only deployed to a war zone once. Had to fight to get to a unit that would send me even. You can head to basic within a week or up to 6 months depending on school dates for MOS and demand for your field. The Army is not a bad choice. PT requirements are the second toughest of the services and if you decide to transfer to Navy or Air Force later, you will not have to repeat basic in their service. All active duty benefits are pretty much the same. I'd have to say medical sucks as far as personal interaction, but that's because there are too many troops per doc. Marines tend to be arrogant after their training. I find they can be really irritating. Ive worked with some Navy and some Airmen. They are pretty relaxed. Just get the rank right and you'll earn their respect. When you deploy, if you run into Marines, address them by their full rank to save yourself a headache.
Anyway, I vote for Active Duty over National Guard. More steady income, and less deployments from your home. National Guard has to do rescue and peace keeping in their state and in other states.
{edit} A good way to get on the sniper path is start as a cav scout. They send a lot of people to SDM school, which is a step towards sniper.