When this question comes up I always say if you can afford it get the Vinson its just better all around. I have several friends wwho asked me before buying and they got Eigers because they were cheaper but they wish at times they got the Vinson one guy I know got a Vinson and he loves it.
The Vinson has rear disc brake, more gc, adjustable shocks, liquid cooled, better lights, big seat, bigger fuel tank, digital display, about 119cc more. Pretty good fuel wise and looks better IMO.
I'm not affraid to put the Vinson to work it pulls whatever I hitch to it and goes where I want to go especially since putting 26" Mud Bugs on. I got 5300-5400KM on it as of 2 days ago since my last ride. I put the bugs on in Oct 2006 and have over 700KM on them now it was like a new bike when I put them on. I have had it up to 98KM/H on the speedo last year and thats plenty fast for me on a 4x4 utility ATV when the guys on the Eigers want to race they get left behind in a hurry even when I give them a head start.
Check out the pics in my sig to see for yourself what I do with my Vinson.

 

We have a 2003 Vinson 5 Speed with 27" Swamp Lites and a 2005 Eiger 5 Speed with 26" Mud Lites. They are both great machines. With the Vinson you get more low end grunt, better styling, more dash features, one extra headlight, and an extra front fender storage compartment. It also has high/low range in forward and reverse the Eiger only has low in forward. With the Eiger you get simplicity with less potential trouble in the long haul having an oil cooler vs. water cooling. You get manual 4wd engagement vs electronic. The ride is smoother on the Eiger and the steering is is also smoother and less jerky in the rough stuff. The Eiger with it's low stance gives much more confidence on hill climbs with no tippy feeling like taller quads. It is the most stable feeling quad I have ever used on steep hills. We have 2800 miles on the Vinson and 1100 miles on the Eiger and have never had a single problem with either one. All of our riding is on rocky Arizona mining roads.

 

My Eiger is great. I am big guy at 250lbs and the bike is quick it does donuts with no problem. During Hunting season we load it with 300 lbs of corn. We have had several deer on it, we had deer tied behind it. It hauled several tree stands at a time most of the time 2 people are on it.. We didn't race the engine but we weighed it down and it just goes. I had a polaris and this is much better it turns so easy.. It depends what you want it for I know I made the right choice

 

Eiger=beefed up lawnmower, which is fine, goes along at around 55-60, reasonable well in the rough. Vinson=beefed up Eiger. I like my Eiger, it could handle the rough stuff better.

 

eiger has no low end, even in neutral, it takes much longer for it to get from idle speed RPM to about middle range RPM, but going from middle to the limit takes no time at all

 

my father owns an eiger, and it is a great erforming machine in ever category for what it is, but the vinny outperforms it in everyway. If your worried about the radiator on the vinny then you have to worry about the oil cooler on the eiger and id rather loose water than oil pressure. The vinny has proven more reliable and i ride ten times harder than the old man and i have twice the miles.

 

I recently had to make a similar choice. I had between $5,000 and $6,000 to spend on an atv and fortunately I found a new '06 Vinson for $5,300 OTD. I spent a lot of time researching and once borrowed a friends automatic eiger and rode it on rocky trails for about an hour. I felt I got a good feel for the quad and felt it would be a good purchase in it's price range. However, several months later the deal on the Vinson became available and I jumped on it. I am so glad I ended up with the Vinson. I know the two Suzuki's are pretty close when compared, but to me there is no comparison between the two. There just seems to be something special about the Vinson which makes it a delight to ride. I've owned several quads over the years, but I always get a certain excitement when anticipating the next ride with the Vinson.