Aside from the obvious differences, State vs. Federal, for the average pilot they are the same. To say that most Guard units are more apt to hire from within, and give local preferences, is probably true, but that varies widely. To go into the reserves, you will have to find a unit that will sponsor you, then your package goes before a federal board. At a Guard unit, it will all take place at the unit itself.
Regarding AMS, all guard applicants, unless prior comissioned, go thru AMS. The reserves send most of their applicants to AMS with the exception of rated positions (Nav and Pilot). They send them to active duty OCS for 12 weeks.
Don't worry about that. From your perspective, you should worry less about it being Guard or Reserves. Apply to any units close to your home first, especially if they have something you would really enjoy flying. The biggest selector for prospective applicants is that they actually believe you will stick with the unit after training. Most of them have a bad history of accepting out-of-towners and they leave shortly after they get their wings. Also, you pretty much need to consider any unit out there. Most have very limited slots, and you never know whose family member, or super-qualified dudes will be applying for your ideal slot. It took me knocking on about 15 doors over 3-4 years to get in, but that's longer than average. You don't want to limit your options because it is not your dream job. Once you are in, the options open up. However, don't go in with the intentions of using a unit as a stepping stone. It will haunt you.
And, most importantly, in-person appearances pay in spades. Just sending a packet in will just get you in the middle of a paper pile. Visit the unit, and get to know the people before interview day. Go casually during a weekend drill. Save the spiffy suit for the actual interview.
Just hit the application process full-bore, and good luck.
