I haven't seen a Win 101 around in at least 15 years - and no, I don't own one.
I think the only rap on the 101 was it tended to break ejectors - or ejector springs .... I've heard talk that the metallurgy wasn't quite up to long term "target" gun usage. I don't think Winchester ever dominated the skeet ranks - but there were a number of them around in the 60's and 70's.
In terms of the 12ga magnum, to my knowledge that just means its chambered in 3" - so you can shoot 2 3/4" or 3" shells. These days virtually everybody shoots 2 3/4" shells for clay target games.
You didn't say what the gun was choked ( but if its choked full ) meaning it was probably intended as a Trap gun - then it won't be much use for Skeet. You'll have to look at the barrel to know whether it has screw in chokes or not. I don't recall when Winchester started putting screw in chokes in their guns - but it was probably in the 1980's. So virtually all of the 101's were fixed chokes / and I don't recall seeing any with screw in chokes - but a lot of them could have been sent to a gunsmith and had screw in chokes put in / or had full length sub-gague tubes added to the gun.
Briley Mfg started in the mid 70's - so it was possible you dad sent that gun to them to have it fit for chokes - and Briley has been one of the big innovators on barrel work since they started.
The gun you describe as a Skeet gun - is probably also fixed chokes - and it may be a shorter barrel length than the other gun. 24 or 26" barrels were common on "skeet guns" in those days.
In terms of which gun would be best for you / look at the overall length, configuration of the stock. If they have an angled stock - one or the other may not fit you without some adjustments or by putting a comb pad on it. If one of them has a Monte Carlo comb on it - meaning its parallel to the rib - then choose that gun. If it doesn't have screw in chokes in it / shoot it as is - or send it to Briley to be fit for screw in chokes.
These days for Skeet - many of us shoot O/U's with parallel adjustable combs - and 30" barrels. All of my guns are fit for screw in chokes - so I can use one gun for Skeet, Sporting Clays or even hunting. In your dad's day - he had a Duck gun, a Pheasant gun, a Trap gun, a Skeet gun - etc and they were all fixed chokes, and had different barrel lengths to optomize what he wanted for that bird or for clays. Today things are a lot different / and sub-gague tubes are also common - which is a way to make a 12ga into a 20ga, 28ga or .410 . Briley and Kolar are the 2 dominant makers of full length "tubes" - and then of course in the end of the "tubes" - you have a screw in choke. For all of my guns - I have 8 chokes 2 Skeet, 2 Improved Cyclinder, 2 Modified, 1 Improved Modified, 1 Full - so they will do everything ( and I have the same for my 12ga, 20ga, 28ga and my .410 ).
Hope that helps a little.
Maybe someone else will chime in - that has shot a 101 .