By 'type' I think we can assume, i.e. a Buffalo nickel Type 1, and Type 2, etc. So, I started with the goal of acquiring a 20th C. type set of U.S. coins, even though I'm a world and ancient collector. Then you can fine tune, i.e. collect 1909 Cents and you have several to choose to make it more interesting. You'll need an Indian, and a Lincoln, with further refinements as to VDB, which I don't consider a 'type' but rather a variety of one type. Find the Best Strike you can afford! To me, for a Type set, you want the best examples of strike to represent the designer/engravers vision. Best condition is nice but then you're buying a slabbers view of a coin that hasn't been touched. I can't say how many times, and years I spent looking for a well struck and preserved 1921 High Relief Peace Dollar, most of which have been slabbbed by now. It's laughable how the slab companies have jacked the value/prices based on their concept of MS theory. You can find an MS65 for a wicked price, nobody has touched it, but the temple locks of Miss Liberty are flat or even mashed in - I'm not paying premium for that! Instead, I found a very nice one that's only MS64 but has seen some contact with the world but the details of strike were way better than the average and makes a great Type, covering Peace and High Relief at the same time, shares a date with the Morgan, pair them up for added interest and it makes a better story in your attempt to show and and attract new collectors to the hobby of Kings, and raises, ever so slightly the value of your collection.