All the expansion packs have the same cards with the same tanks. So the 2 Sherman packs will have the same cards. Each tank pack has at least 1 card you can't get elsewhere (I believe?). That said, if you're looking to get cheap tanks, 2 starters is a great way to do that.

I should point out that the sher man and Panther expansion do include unique cards not in the starter set.

Each expansion has different cards but if you were to buy say multiple Panther sets, all would have same cards.

Also, most kits can make multiple types of tank. For example the Panther sprue let's you make either a Panther tank or a jagdpanther.

In fact with some kits, if you use some common sense when assembling the model you can actually get both variants. Can only use one at once but does give you options. The sherman and Panther kits are two examples of this neat trick.