Which series? There are way too many and which site is the best to purchase from? I plan on buying it online but if there are great prices on stores, let me know!
If you want a tablet , buy a ThinkPad X230t.
If you want a workstation , buy a ThinkPad W530.
If you want an Ultrabook , buy the X1 Carbon.
You can use the B&N Gold site or another EPP site to get discounts online that would make the price way better than buying in store (if you can even find them in a local store).