When I was looking for a ski bag, I used online forum (like this one) as a guide. But I don't solely rely on this, I also pay attention to what skis bag travelers use at airports. From these 2 sources, I formulate my own criteria.
1) My first "real" ski bag was a double Sport Tube - holds 2 skis. I decided on this because of what I learned from this thread and another forum discussion. I saw good review for Sport Tube. I know I need a bag with wheels for ease of transport. Double ski bag so I can stuff additional things inside the tube. Plus I was planning ski trips to Canada and I heard that Air Canada only allows hard shell ski bag...
But it turned out Sport Tube was not for me. Too heavy and I pulled my muscle from hauling it during one of my trips. Plus it was not the easiest to pack. I sold the Sport Tube after used it for one season.
2) My 2nd ski bag - I got a soft shell ski bag - Oakley brand. Main reason, most travelers (~80%) I saw at airports, they are using soft shell bag. If majority of people are using it, there must be a good reason. I got one with wheels and it can hold 2 skis.
I only look for bags that can hold 2 skis even though I only own 1 pair of skis. This is because, if I travel w/ someone that don't own ski bags, theirs can put in my bag.... (It turns out few of my ski friends that I travel with, they don't fly out west for ski trips, so they don't own ski bag). Also, I learned from this website that, if I happen to buy a pair of skis in my trip, I will have "room" to fit in a 2nd pair.
3) My 3rd ski bag - While Oakley ski bag works fine, it's pretty heavy (self weight). Then I saw
@Rainbow Jenny mentioned Dakine snowboard bag that she used as ski bag, it can fit up to 3 pairs of skis (if bindings are removed) and it is light weight. To my luck, I spotted this Dakine ski bag at a REI garage sale, so I bought it. I haven't used it yet, so the verdict is still out.... But I do like Dakine bag because it is light in weight and shorter than the Oakley, it will be easier to haul around...
4) At one point, I did consider to get the DB double ski bag. But the review I saw was not so good, specially about the materials they use... so I stop looking for DBs.
What i learned from this searching process, it takes few trial and error to find the perfect bag that's the best fit for me. Online review does offer valuable information, it helps you to narrow down the search criteria. It is usually helpful to observe what other travelers are using because not all folks post what they like / don't like on online forum.
As for "rolling duffle" bag, this will be my next purchase. I am still looking and haven't found anything to my liking. So I will keep my eye out and also pay attention to online discussions about this topic.