Definitely Troll Battle Wheel. While I'm not a huge fan of both of these sets, I'd have to go with 7041. I loved the Fantasy line so, so much. They have a special place in my heart.
Let's be real, who doesn't love a mass amount of Dark Brown plates too?
Troll Battle Wheel wins, without question. I probably get more comments and attention given to my Battle Wheel than any other lego set in my collection. It is so unique and silly that it demands an explanation . To top it off, the triggering mechanism allows the whole wheel contraption to be held/aimed like a pistol--it's a good thing I didn't have that as an 7 year old or I would have been putting out eyes all over the place. The crazy thing is I was given the battle wheel as a gift and probably wouldn't have paid for it when it was available.
The Viking set has better figures and is more realistic, but it doesn't stand out in any significant way beyond the figures.
I think here speaks my steampunk-affinity: of course I prefer to totally impractical, crazy and oversized troll contraption! Such craziness just deserves credit! As long not all sets end up being completely over-the-top, but something freakish here and there is very welcome.