I'd do both. I'd sell everything at the garage sale first, and then I would take anything that didn't sell to a consignment store. While there's no guarantee consignment will take it, this way you get first crack at setting your own value on the items at top dollar. You can always lower your price during the garage sale if things things don't move because people think you're asking too much.
I have done this myself, and I can tell you... I always make more money at my garage sales than I do selling to consignment. You have to remember, you're in essence splitting the cost of the sale with the consigner. They always get the higher percentage, or they won't profit. So I figure, cut the middle man out first, and if that doesn't work what do you have to lose? Afterall, the only plus with consignment is if they do take the items, you're getting a guaranteed check/money for the items. But its not necessarily the most you could get for the items.
As for setting the price on items to be sold at a garage sale, I usually set it at 40 to 50% what I paid for them brand new, if they are still currently available in stores, and are gently used.
If they are new in the box or packaging, I knock off just about $5 the orginal price. If the items are much older, but in good condition, I'd set the prices on par with what you'd find in a second hand shop (under $10).
With the particularly nice garage sale items, I have found people are willing to pay if the items are about 50% of the current selling price in stores. Before the sale begins, I will keep a lower price in mind that I'm willing to let it go at, and will barter to that point if someone is relunctant to pay my original price. I will try to base my lowest final price on par with what I'd expect the consignment store's payout rate to be. That way, you at a minimum will save yourself a trip to the consignment store, and make what you would have made anyway.
You'll find most people who shop garage sales love to barter for their bargains. Especially if the items you are selling are in great condition. I think serious garage sale goers expect this, so you should, making it all the more reasonable for you to set the prices a little higher. When putting up an ad in the paper or on-line etc., be sure to include detailed description of what you will be selling, including brand names, sizes etc. The more details, the more "good gets" the more serious shoppers you'll get. Location of the sale is no obstacle. What you sell is the big decider. Name brands, collectibles, hand crafted, etc. are all words that will bring potential buyers.
Once again, there are serious bargain hunters who spend their entire weekends mapping out the metro for the "must go" sales in the metro. In the past, I've even had die-hards come to my house the night before while I'm still setting up so they could have a private "showing" of what's up for sale. And the next morning, hours before our "doors" open, people camped out front waiting to get first dibs.
The big challenge with taking GS items that don't sell to consignment is keeping it clean and presentable so they still get a good price at a consignment store. I'd keep this in mind as you plan on where you'll "place" the items, and how you'll present them. I'd try to hang everything on hangers, and keep them away from the elements and blowing dirt. Putting clothing items on tables migh encourage people to touch them, ball them up or what not. The hangers will keep them off the ground, and make them easily viewed as complete ensembles.
Items like high chairs, strollers, or toys etc. will do fine on tables etc, but remember to remove garage sale tags before taking them to consignment.
Hope this helps. Good luck