Deli sliced lunchmeat will likely be loaded with a lot of the same preservatives as the packaged stuff you buy in the grocery store, but not always in as high a quantity, since the loaves that are sliced in the deli do not require as many preservatives. There are a plethora of different products on the market, and it just depends on what the deli case stocks.
Here is an example of the dizzying array of choices:
http://caloriecount.about.com/tag/food/lunchmeat
There doesn't seem to be much difference between the fat and sodium content of the turkey and ham; overall, if you make sandwiches with any of the sliced lunchmeats, I would go with the thin-sliced, and use lots of lettuce... If you are using mayo, go with low-fat options; yellow mustard is even better, most brands containing zero fat and cholesterol (Compared to mayo, which is basically oil and eggs).
If you're like me, you need a slice if cheese on your sandwich; good old American slices have 60 calories each, so you might want to look for a low- or no-fat cheddar or mozzarella. And whole-grain wheat bread, or Wonder if you must have white bread.