Don't know where you're from Model 12, but over the years I've found that the 4-5/8" bbl'd models carry a heck of a lot better for me. We live on a farm and I'm often on a tractor, lawn mower, horseback and even the Jeep and that short barrel just does not push the gun's stocks up into my ribs like the 6-1/2" ones or even the the 5-1/2. I've got RUgers in all three of standard length and the shortest is by far my favorite; the others have been relegated to range use only. As to the accuracy argument, it's just not that apparent in actual use. The 4-5/8" vs. the 6-1/2" accounts for barely 1/2" on target, from rest at 25 yds. At extended pistol range, say 50 yds or beyond, it'd make a difference, but not inside 25-30 yds.
I've got a pair of Ruger .44 Specials in the short length as well as a New Vaquero in .45 Colt...all are more accurate than I can shoot them. But the NV needed to have its throats opened up to a uniform 0.4525" to shoot lead alloy bullets with any accuracy (3+" before work and <2" after). I can't say if Ruger had finally decided to machine it's cylinder throats to make them compatible with the groove dia. but it's a factor to be considered if you go with a .45 Colt convertible.
I make all my own leather, preferring for the most part, my own copy of the old Tom Threepersons open top, strong side model and with minimum drop at that. The weight of a full size Ruger, short or long barrel hangs well from an 1-1/2" belt too. El Paso Saddlery makes a fine copy of that old design and the belt as well. A good belt BTW is essential for comfort when carrying
So if you plan to carry your new Ruger, for field use with a strong side holster, I'd opt for the 4-5/8" model...with a minimal drop holster...that's the ticket.
Here's a cpl pics, albeit with a 2" home made gun/money belt. That's my copy of the Tom Threepersons holster. The 2nd one is of a Single Six .32 with a 4-5/8" bbl. in another Threepersons holster. Rod