As for barrel length, I prefer an 18" or a 20" round barrel on a rifle. It still allows for a full 10 rounds, but does not have the out-front weight of a 24.5" or larger. I particularily like my Marlin 1894 trapper in 38/357 with a 16" barrel, but you can barely put 10 rounds of 38 in it and only if the lead is the right length. Marlin trappers are hard to find, and stay away from Win 94's as they were never meant to handle pistol calibres - they work in practice but not under pressure.
With pistols, I have both 5.5 and 4 3/4. Stay away from anything longer as your hands will tire faster and they are slower out of the holster, although they do help keep roll in your hand to a minimum with the extra weight out front. I prefer the 4 3/4, but it is a personal thing, and the weight diference with the extra 3/4 of an inch is negligible. Once again though, the pros all seem to use 4 3/4 so they must know something.
While you didn't ask, I will pass on some thoughts as to makes and models. Some people swear by the Rugers, others the Uberti's. Some use the Beretta's but not too many. The Pietta's have been getting good reviews, and are supposed to be as good as a Uberti but less money. My suggestion is to stick with the Uberti's. They are good and strong out of the box and strong enough for the weekend warrior. Furthermore, any good gunsmith can smooth them up and lighten the springs for around $100. I haven't heard about anyone doing much to the Pietta's as they are very new, and the Beretta's well few people seem to use them. As for the Rugers they are extremely strong, but look in the magazines ... everyone seems to be modifying them to act more like Colts and Colt clones. Why not just buy a Colt clone like the Uberti?
With rifles, I love the 1892's both my originals and copies. However, they have a few idiocycricies that are not the best for new shooters, plus they are a pain for the average gunsmith to work on. The Uberti 66's and 73's are good but very expensive and require gunsmithing to be smooth, but you can get race parts for them if that is your target. The best guns out of the box, that can be tuned for $100-150 are the Marlin 1894's. They are reliable enough for you and I, relatively smooth for stock guns, and relatively inexpensive. Keep in mind that while a new gun might cost a little more, you will know what you have and should have a good life span. Any gun that has already been used for CAS may be worn to the point of costing big dollars to rebuild (kind of like buying a new car vs one that has high mileage but no odometer to tell you the exact mileage). Guns that have been used for target shooting are one thing, competition guns are another.
Just my 2 cents worth.
JB