Both are good choices, both have excellent quality and both have roughly the same tools. I think your choice is going to come down to a few things: Price, Size, the sheeple effect, Locking Blade, and Small Blade. For some people price is a big concern and at about $30 difference between the knives it can be a deal breaker, for other people price is not a concern.
For some people the 18mm is the difference between comfortable pocket carry and uncomfortable pocket carry, sheath carry will make this moot. The difference in size can also be important to you based on your hand size, most times people with bigger hands like a bigger knife because it fits the hand better, likewise with smaller hands and smaller knives. If you can carry the larger knife in your pocket comfortably and it is comfortable in your hand, then getting the larger one is no big deal, if it isn't though you should get the smaller one. One other thing about size, these are both thicker knives and as such many people find that they are harder to hold, even if they have big hands, if you find the either knife to thick then you might want to reduce the tool selections down to what you really need (adding a small keychain Vic or Wenger with scissors might be another option).
Larger knives are scarier to sheeple which might be an issue if you are traveling and using the knife when around people, the smaller one will cause less problems.
The large one has a locking blade, the smaller one does not. The smaller one has a second smaller blade the larger one does not. Sometimes it is the small things that make your choice for you.
I'm also going to suggest that you look at the Wenger knives (since they were bought by Vic the quality has attained the same level as the Vic knives). There are a number that are similar and maybe you might like them better (I switch my EDC between a Vic Camper, Vic Farmer and an Wenger Evo S17).
http://www.wengerna.com/browse/browse.jsp?cat_id=1&sub_cat_id=75
