These are some tough questions. There are so many options at PCKS, its hard to choose. I guess thats why some people have so many different PCKS Bucks. Ill try to highlight a few finer points, but much of this is personal preference.
Finger grooves / no finger grooves I cant help you here. You either like them or you dont
Rivets / no rivets Rivets hold the various handle materials onto the frame of the knife. The No Rivets options uses glue. The rivets are probably more sturdy in the end, but dont look quite as nice.
Handle materials This is a big personal preference deal, as this feature determines most of a knifes aesthetics. Wood is a good sturdy material, but no outrageously waterproof. Stag and bone can crack when dropped hard, but provide a nice grip. Id say that horn and bone are wonderfully waterproof and wear resistant.
When it comes to steel selection, intended use is the key. BG-42 is a sensational all around steel. Actually, its my favorite steel. It sharpens pretty easily, and takes a wicked edge. ATS-34 is also good, but not like BG-42. 420HC takes a good edge, but doesnt hold it as long as BG-42 or ATS-34. The 420HC is whats used on a standard Buck110. Its nicely stainless. The BuckCote steels, if memory serves me right, are chisel ground blades. Chisel grinds have pros and cons. I wouldnt get one without first studying up on their strengths and weaknesses. Damascus steel is gorgeous looking, and great for a mantelpiece kind of knife.
Serrations Again, this is all about what the knife will be used for. Study up on serrations if you dont have a complete understand as to their usefulness.
Bolsters Whatever color you like. The brass tends to tarnish a little faster than nickel/silver.
Engraving Heck, its cheap. Just dont engrave your wifes name on it, unless you plan on giving the Buck to her as a gift.
Sheath type You can handle that one without my help.
Just for the record. Heres what I ordered:
Stag, fingergrooved handle, without rivets
Serrated BG-42 blade
Brass bolsters
Black leather sheath
The knife was sent back afterwards for engraving
I love this knife!!!!