Re: Most collectable sniper rifle
Go for an unpapered (non-DCM/CMP) M1D with an M84 scope and a cheekpad. Don't worry about the flash hider and other junk because you won't want to shoot with them anyway. Get it bedded and do a trigger job--best of all worlds. The nicer ones are running for about $2400. CMP is selling M1Ds for $1500, but the scope, mount, and cheekpad are going to put you back at $2400 for a total outlay if purchased separately.
If you shoot it with the Hornady Garand load, you will have accurate and historic. Also, you will see many disparage non-papered M1Ds. Many of the papered M1Ds are just late arsenal put-togethers without any history behind them. So, you have to ask yourself how valuable that piece of paper will be for your shooter. In contrast, most of the M1Cs and M1903A4s likely saw service as snipers, so it would be a small travesty to beat them up.
I shoot my 03A4, but I don't shoot it much. My goal is to have less than a TE of 4 before my son gets it in my will. (Or, find a replacement barrel...) Good middle ground may also be to get a 1903A3 that has been drilled/tapped into a 1903A4 configuration--that should cost you about $1500 to do right.