If I was buying one, it would be the Magnum. ...But it all depends on the way you would use it.
I would use it for rabbits, squirrels (not for eating), prairie dogs, and various other varmints and small predators. In those instances, the .22 WMR can be amazing.
But, as a "fun gun"... .22 LR is far cheaper to shoot. ($2-3 /box of 50 for .22 LR vs $10-17 /box of 50 for .22 WMR.) And... some of the "premium" loads for .22 LR can be quite impressive ($5-7/box for Stingers, Yellow Jackets, Mini-Mags, etc), still at less than the cost of non-premium bulk ammo for the .22 WMR ($9-10/box for Win Dynapoints, ArmsCor, Fiocchi, etc).
I love my .22 WMR. But if you don't need the extra performance, it's a very poor financial choice for a plinker ("fun gun").