1. Both are good, but it depends what you want the gun for. The external hammers have to be manually cocked before shooting, so if speed of operation is desirable, this is a downcheck. On the other hand, they're more "authentically" old-style, so if authenticity floats your boat (e.g. SASS), they have an advantage. Also, bear in mind that for some years, the Baikal external hammer guns were not true external hammers at all... they were basically cosmetic, with the firing pins still functioning internally. Only in the past year or so, IIRC, did Baikal come out with a true external-hammer gun. You'd better check whether the ones you looked at were the new style.
2. Rugged as rugged can be! A gunsmith who smoothed one out for me said that it was built like a brick outhouse - massively over-engineered. He said that it had more redundant steel than any other shotgun he'd worked on. This is a negative in terms of weight, but a strong positive in a gun that you want to have around for a long time - it's very unlikely to wear out!
3. Overall, I liked mine (a 20" internal-striker model). It badly needed a trigger and action job, as without these it was very stiff indeed. However, with smoothing-out, it was a pleasure to shoot. Unfortunately, I no longer have mine... I loaned it to a friend, who took it with him on a 3-month trip to see his grandchildren. He died while there, and his family sold off his possessions and/or kept them themselves. They wouldn't believe that it wasn't his gun, and so rather than go into a long and costly lawsuit, I left it with them. One of these days I'll replace it.
I've also owned the Stoeger 12ga. double-barrel coach gun, and this was very nice (better action "smoothness" than the Baikal out-of-the-box), but I think less strong. I'd buy either, but if I have a gunsmith available to work on the Baikal, this would be my first choice.
