Generally, futures are worthwhile only in very good years, like 2000 and 2003. Sometimes, in less than stellar vintages, the wine may be cheaper upon releases than it was as futures. That being said, it is exciting when that phone call, e-m, or letter comes telling you that your wine is in and already paid for.
Where you order your futures from also depends on where you live. If you live n a state like Florida that does not allow wine to be shipped in from out of state, how will you get it home? If it is to be shipped to you, factor in the shipping costs because some merchants ship for a lot less than others. Large merchants usually have the best shipping rates because they receive volume discounts from UPS Fedex, etc. You also would have to make special arrangments if you wanted to get those nice wooden boxes that the wholesalers or stores may get it in. They really won't work for standard shipping.
Factoring all of this in, it is often easier and cheaper to get your futures locally, if your wine merchants offer them.
I have gotten bordeaux as futures from Wine Club (Santa Ana), wine Exchange (LA), Zachy's (NYC) and McArthur's (Washington, DC). All have large selections. Not all places have the same wines, but most have the big names. My preference for reading and deciding about the wines I have ordered is the Wine Advocate.