I like the M1-A very much, but the design is over 50 years old (1957 Adoption by the military IIRC). hey are great fin to shoot, so whether you buy one of those, or a newer design is up,to you.
to be sure, you can do a great deal of work tricking one out, but if you trick out a newer design, you will have a nice rifle there too.
I would evaluate the following to help you
1. What do you want the rifle to do?
Shoot on a range, or be a fighting tool?
2. Cost of any modifications to each system.
3. Availability of rifle, magazines, spare/repair parts, optic mounting systems and costs...who can work on the rifle?
4. Durability of each system
5. Interchangeability of parts and magazines with other systems around you
6. Do you want a standard cartridge(7.62x51) or something different (6.5 Creedmoor)?
7. How much do you anticipate shooting the system( back to durability and maintenance costs)?
Also, if youmscopr the rifle, the M1a stockmismdesigned for iron sights..a scope requires modification or adjustment unless you use an E2 stock. Even then, you might still need modification to the stock.