Those are both great guns. I have a Mini and would really like a Marlin 1894.
The new Mini 14s are much more accurate than the old ones. Attached are my last two groups from 50 yards.
By the way, for just plinking, the Marlin will cylce most .38 special rounds just fine. And since .38 is around $16 per box of 50 ($.32 per round) this is pretty significant savings.
http://www.midwayusa.com/viewProduct/default.aspx?productNumber=394204
Ammo cost for .223 is about $9 per box of 20 ($.45 per round).
http://www.midwayusa.com/viewProduct/default.aspx?productNumber=786237
I agree with what gtscotty says, and I would add the thought that if you primarily want to do shortrange plinking, get the Marlin. If you want to be able to reach out a little bit farther, get the Mini.