I have the Tillia Food Saver Professional II and couldn't be happier with it. I have been on the Yahoo groups for vacuum packing and it gave me tons of info. One thing that I learned there is that the Tillia brand is pretty much the only one worth the money. The rest do not work well and with vacuum packing it either works or it does not.
Check out the group here http://groups.yahoo.com/group/FoodSaver/
Start at the first post and work your way forward. All of your questions will be answered.
One thing that I think is important is to get a unit that has an accessory port. This lets you use foodsaver canisters as well as regular mason jars to seal things. Without this you are stuck just using the bags which can be expensive. The canisters are expensive too, but they are reusable.
The professional II model that I have has a number of features that I really like. One is that to turn it on I just push a button. I can then walk away and it will turn off on its own when it is done. Some of the other models require you to hold the lid down then whole time it is running. For small things this is no big deal, but for larger jobs I would find that to be a pain in the @$$. Another feature I like on the pro II is that it has a built in bag cutter and bag storage. One of the draw backs though it that it is pretty big. I think you can find other models that have these same features, but takes up less space on the counter.
Well I could go on and on about this thing. I use it every day and it is one of those things that I do not know how I lived without it. If you have any other questions I would be more than happy to answer them. Check out the Yahoo group though. There is so much specific info there that you would not believe it.