All Vikings share a similar grind/moisture: a bit finer/dryer than "medium" in both cases, but they tend to feel very silky and are easy to take.
Dark: Deep fermented tobacco, briny, leathery, a bit of tarmac. This is a top-5 tobacco for me.
Brown: Similar to Dark, but less extreme. Not quite as leathery or tarmac-y, but still a "dark" snuff.
Blonde: I have no use for this, except as a base for home scenting. It's easy to take but it's practically scentless. I guess if you need the nicotine but don't want any aroma it's ok, but it's a non-event for me.
Thor's Hammer: The aroma is similar to, but a subdued version of, Dark and Brown. It gives you the punch without being overwhelming. Stronger in nicotine than dark (I think), but not stronger in aroma.
Peach: Well...it's peach.
Spear: Spearmint. No menthol added, so if you like something cool without menthol this is solid. It's on a dark tobacco base (similar to Brown, I think), so you mostly get Wrigley's gum followed by an undercurrent of dark tobacco.
If you like one of Dark, Brown, or Hammer, you'll probably like the others in that group - it's just a matter of which you like the most.