Without a doubt the M1903. I would say of the M1903 series the 'A3 because of the sights.
And they were still being produced after 1940 if we want to get picky.
No we can all have our opinions or we can look which rifle outscores the others at the CMP Vintage Military Rifle Matches.
Excluding the Vintage Sniper (where M1903s rule) and the Carbine Matches, you have the Garand Match, the Springfield Match, and the Military (all other) Match.
Check the CMP Website for the scores of the different matches. The Springfield Scores are high on the average (which is why they have their own class).
The CMP gives Achievement Awards for certain scores. Gold, Silver and Bronze. Out of a possible 300 pts.
For the Garand
Gold 281 +, Silver 273-280 Bronze 264-272
Springfield
Gold 282 +, Silver 274-281 Bronze 265-273
Military (all other)
Gold 277 +, Silver 269-276, Bronze 257-268
The Garand as we see is a close second to the Springfields
There are exceptions of course, you can find some good Military rifles and you can find some bad Springfield Rifles, but on the whole the Springfield rules the roost.
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Vintage Snipers are pretty much the same. Normally the 1903s win, except the Cody CMP games. The M1 series sniper rifle won out. 2nd place was Springfields, that team came in 2nd even after saving around.
Wheather the A4 or the A1s are better is dependent on the shooter. Personal I tried the 8X scopes, I prefer the 'A4s but it has to do with my High Power Background using open post sights. For that reason I like the post in the scope of the Weaver K 2.5 or M-82. But that is personal opinion on my part.