OP, these guys will beat you to death with their personal desires.
The big thing about collecting is that there are different wants and needs for every individual collector.
I know a fellow, now deceased, who collected P38s and P08s. They had to be mint, unissued or he considered them to be junk.
As for which grade of rifle shoots better?
It works this way. Some rifles shoot better than others, that's life. I've had the opportunity to take ten new in-wrap Mauser 98s out of the crate, clean them and shoot them with period-correct, issue ammunition. Same ole, same ole. Some of them shot very well, others shot acceptably within the specified requirement.
I've seen FTRed rifles do exactly the same thing.
This is what it all boils down to.
Most, not all of the unissued and FTRed stuff is long gone. There may be some squirreled away in government storage facilities, but they're almost impossible to find, let alone get them out of government control.
That means what's in civilian hands is all there is and there won't be any more coming.
Old farts, such as myself are getting long in the tooth and are starting to sell off their collections.
I noticed this at the Chilliwack show last week. There were close to 600 tables. It's now the largest show in Canada.
At least a third of the tables were covered with milsurp rifles, including muzzle loaders, early black powder cartridge types, just about everything still legal to sell that saw service beyond the Viet Nam War.
hundreds of Mausers, Lee Enfields, Sniders, Springfields, SKSs, Garands, etc.
Ammo was available but expensive.
There were dozens of newbies, fondling everything and lamenting the prices.
They had to be careful, lots of the firearms on those tables were not FTRed by any government armory. Many are put together with surplus parts.
Don't get me wrong, for the most part, they're very well done and it's pretty easy to tell what they are. Many are beautiful and a lot of care and time has gone into them. Some??????????
Most of the put togethers, were selling anywhere from $800 to $1100, depending on the condition. Anything original or gone through an arsenal FTR started at $1200 and went up from there.
My advice to newbies is simple. First, decide what you want the firearm for.
Do you want to collect/display without ever shooting it, or do you want to collect/display/shoot it, or do you just want it to participate in the "fun shoots" for milsurps at your local club?
Are you looking for a milsurp that cheap surplus ammo is still available, are you going to hand load, or purchase commercial ammo? None of the options are cheap anymore.
So it all boils down to which level you're going to participate in and that is often limited by what you can afford.
When I started, close to sixty years ago, I had some very unique opportunities which allowed me to cherry-pick from thousands of each type and purchase at distributor cost.
Most people don't have such opportunities.
My collection is now down to filling one safe. My gun room is mostly empty. That's OK, now it's "someone else's" turn to take care of the gems I sold off over the past ten years.
Just purchase what you can afford. If you're holding out for the "holy grail" at dirt cheap prices, scour the "yard sales" You might get lucky but don't hold your breath.
Gun shows are not YARD SALES.
Don't get the two confused. You will be disappointed.