AR15, I guess. It's certainly not ideal for any particular role, but it can get the job done on a variety of tasks.
hunting
I'd be hesitant to hunt whitetail with an AR, though there are some who claim it works well for them. .308 or .30-06 are great for deer-sized game, and a bit larger with range limitations.
home defense
AR, of the available choices. the .30cal rounds, in addition to being absolutely deafening indoors, are
way too over penetrative at the point blank ranges we're talking about. I'd be very concerned about liability -- your neighbors aren't likely to be too keen on the extra ventilation you will install in their homes at 2am. The same arguments can be made to some extent for .223, but SWAT teams load them up with light, expansive bullets and it seems to work well for them.
plinking/shooting in general
Shooting an AR at reactive targets can often cause severe cases of "Shooter Giggling Like a Little Girl." It's a fun rifle. Garand shooters tend to go for little groups, which can also lead to BOG (Big Ole Grins). I don't know about M1As, but I bet they're just as enjoyable.
A pistol/shotgun combo is my preferred HD arsenal, I've got a scoped 10/22 for plinking, and I'd prefer a lightweight bolt action for hunting deer. I like my guns to have some semblance of purpose in filling a niche (as does my wife
), so I suppose I'd get a Garand -- niche: rifles of historical importance used to rid the world of facism. Think she'll buy it?