If it's primarily for groundhogs and secondarily for deer, go with a .243 Win or .243 WSSM. But if I wanted a light deer rifle, I'd go for the .25 WSSM. If someone other than Browning had offered that caliber for lefties, I'd have given it serious consideration (heard too much about feeding problems with brownings on this forum; especially with handloads).
There will always be comments to the effect of "Why get this-n-that when such-n-such will do the job just as well with less recoil, wider bullet selection, cheaper to shoot, etc." It's all well intended, but if you've got your heart set on a super short magnum or any particular caliber, don't give up too easily. They all have pros and cons and in the end, most all will get the job done (unless you're going after seriously big and/or dangerous game).