I'd personally go for a Garand or a Lee-Enfield. And of the Enfields, I actually personally prefer the earlier SMLE/No. 1 Mk. III* of WWI, the the No. 4 of of WWII, though the No. 4 is probably objectively the better rifle (apart from having a crummy bayonet, which is a pretty minor gripe). The No. 1 Mk. III* is still a WWII rifle as well, however, as not only did the British use them early in the war, the Australians never adopted the No. 4, and kept making the No. 1 Mk. III* at the Lithgow Arsenal right up to the end of the war. Ditto for the Indian Army, who kept making the No. 1 at Ishapore into sixties, and in 7.62mm NATO at the end (these have crude, blocky-looking nose caps). I also really like the M1917 Enfield (which saw some very limited use in WWII -- many were even sent to Britain to arm the Home Guard), though it's very difficult to find them with decent bores.
After the above-mentioned rifles, I probably like the German K98k Rifles best of the WWII guns, and the German G43 would be lots of fun to own. The holy grail of WWII rifles for me would be either an FG42 or MP43/StG44, which are NFA guns and will cost a mint to own, even if you can ever find one for sale.
I've never been overly impressed with the Mosin-Nagant. I don't think they are very pretty guns, like the Springfield, or so-ugly-it's-pretty like the SMLE; they're just ugly. They're also pretty crappy in the ergonomics department, to be perfectly frank. Don't get me wrong; they're rugged, reliable guns, and many are very accurate, and both the Finns and the Russians did heroic things with them. But I have never been moved to acquire one. If I ever were to get one, I'd prefer one of the Finnish ones, which are nicer, but I'll probably never own one. There are too many other guns I'd rather spend my money on.