I like both, and own a few of both types.
The Ruger sets the standard with its transfer bar system, and I've never had one to fail in all the years I've been messin' with'em...and that's been a while.
The traditional hammer down on empty chamber can be safely carried with a full compliment, but does run the risk of damaging the hammer nose...aka firing pin...if dropped. Just lower the hammer with the nose between chambers, resting on the edges of the brass rims. Needless to say that it works best with revolvers chambered in .45 Colt and .44-40 WCF...but will also work with .44 Special chamberings, though the nose isn't cushioned as well in that caliber.
Note that this is usually considered a short-term option..when expecting that the gun will be used presently, and the need for all six rounds is a distinct possibility. For long-term carry...or carrying in rough and tumble conditions...the gun should be returned to 5 round status.
In my opinion the transfer bar is safer because it eliminates any confusion or human error as to which chamber to lower the hammer on.....
While technically true, especially for those who tend to let their attenton wander, the tried and true method is pretty foolproof as long as the procedure is followed precisely. As CajunBass outlined...Load one, skip one...load four. Close the gate. Cock the hammer and lower it. It will be resting on an empty chamber...every time.
I love the traditional SA revolvers. There's just something about that firing pin on the hammer that appeals to me...but the transfer bar system is the more practical of the two in a working gun.