You have heard just about every variant of advice, and all likely more sound than mine, but here are my two cents to confound further your selection.
Perhaps interest, budget or family constraints will prevent you, but the "buy em all" advice from THR-brethren comes from a shared experience, that once you have one, it tickles a historical passion that generally leads to expanding a collection: towards a gaggle of Mosins, admiring the simplicity of the action compared to the performance of the rifle, or expanding from the first nation to a fine sample of each nation, or developing a particular theme you follow.
What I enjoy about WWII rifles, is that in those times pre-globalisation, the individual characteristics of the nation, its culture and its people are fully appreciable in the weapon itself. And by firing and maintaining these weapons you connect to the history which we must not forget (if the lessons of wwi and ii are forgotten, in this time of crisis and technology we risk truly becoming lost). Today's weapons, like today's cars, have reached a fairly common technology based high level of performance. But while you have price determined feature and performance, they are imho a bit the same in the same calibre. However, those weapons, by the 30s to the late 40s had reached a technological state of the art, but still relying on an individual engineering fully incorporating the thought and soul of the culture from whence they sprung.
A Mosin is.... soooo Russian. Direct, uncompromising, powerful, simple, but its boom and recoil and flame (while punishing on the shoulder) are Tolstoy, Pushkin. Brash and poetic. Brutal and romantic. The simplicity of its trigger, bolt, bolt carrier, barrel bands, sight post, stock and stock assembly (even compared to my cheapo winchester 190 22 which is a pain to disassemble) are just awesome, in the literal sense, when you consider the incredible millions which were manufactured to win a war fought with volume. It connects you to the fact of history, and through that to history itself, and through that to mankind.
Hey, imho imho.
The Gustaf. Understated and yet so very efficient with its flat 6.5 cartridge. I lived in Sweden for 7 years and this rifle is... SWEDISH. Gorgeous elegant streamlined shape of the rifle, beautiful wood, technologically advanced action, practical visible safety. Information Transparency... Can you imagine a Russian or American rifle with detailed information stamped to the side about the quality of that particular rifle?? No way.
The Lee Enfield: am I pushing the stereotype to describe how unusual it is to note the asterisk denotes it was manufactured outside of Britain? It is simultaneously inclusive and accepting, like Britain, while also segregating and to some degree classist. Of course every country had varying manufacturing places and processes, and almost all sre identifyable, but I know of none as rational and systemstic as the Enfield's. And it is a polite firearm. I find it ergonomic, quick to sight, extremely fast to cycle, smooth, and powerful, and accurate for a battle rifle. All the qualities of an excellent and polite firearm. One cannot complain. The Enfield would not have been designed in Italy.
Absolutely I am somewhat tongue in cheek (only a little) and these are gross stereotypes, perhaps rationalized only after the fact. But for me these historical connection is a powerful urge. This was the war that defined modern Europe, the one that set the stage for the modern American empire, the one that fundamentally transformed the course of Asian history. The battle rifles that were tools of these massive transformations are so much more than just a rifle.
That said, here are my recommendatioins:
#1 The battle rifle of your country or ancestry, embodying the history of your culture. If that is a non-European linked pure "American"' then the Garand is a semi-automatic you should not discount. It was the most technologically advanced rifle of its kind and you will have ZERO regret at not having bought a bolt action. If you are of a different ethnic origin (chilean, argentine, persian, german, spanish, etc.) the Mauser had so many variants, you can probably find one that probably captures your history, and that one can take pride in. Or perhaps you just have a passion for a certainn country's history. But buy the rifle that sparks your interest and history. Get something you cann connect with.
#2 The kar98k: pinnacle of the mauser lineage, and the mauser is the pinnacle of the bolt action. I cannot find one in my budget, or I find one at the wrong time, so I do not speak from experience, but I still think every WWII collection starts and ends with the Mauser of Mausers
#3 The Enfield: Just a great rifle. 303 british is widely available and cheap, even in match cartridges. Yes, surplus ammo is exhausted which means it is not as cheap as others. I cannot comment on US ammo market. Here, it is my cheapest commercial rifle ammo. It is extremely fast and smooth, and something about the scope of Use from Western Canada to eastern Australia, with every part of dust and sea between, is tremendously significant from a historical perspective. It is still a battle rifle in use today!
#4 Mosin Nagant. Maybe this should be number 1. Read Antony Beevor's Stalingrad, and then his Berlin, watch the movie Enemy at the agates, then buy a Mosin and clean it and fire it and reflect othe courage suffering and glory of those millions.
Plus they are cheapmand fun to shoot and some of them can, despite all their simplicity be very very fine shooters.
#5 The Arisakas... I know nothing about them, but you mention two, so there is an interet. Why not start there?
ENJOY whatever you decide. Best of luck.
