More info needed. How much do you ride now and on what sort of bike? How much do you know about bikes? How adept are you at repairing bikes? How much are you willing to spend to have someone else repair a bike for you?
A few points: used bikes Can be great values---or huge money pits. If you buy used without inspecting the bike ... good luck. You cannot inspect bikes bought on EBay. And if you get a Craigslist bike, you can inspect it---to the limit of your inspection skills. If you buy a used bike, it might be a garage ornament being sold for a third of its value after years of taking up space---or the owner might have slapped a couple new tires and a coat of wax on an old bike. Doesn't mean the bike might not have a lot of life left .... might or might not.
Also ... high-end gear from 10 years ago is about on par with mid-low gear today. A nine-speed Sora group is as good as 10-year-old Ultegra ... and has ten years more life in it. Ten-year-old carbon fiber probably weighs as much a high-quality new aluminum and might have stress cracks you won't find until the frame snaps. or, the frame might last for the rest of your life. Roll them dice.
But just because it is CF doesn't mean it is better than Al or steel ... or even necessarily much lighter. An old or cheap CF frame might weigh more than a good modern Al frame at the same price point.And unless you plan to race seriously, a pound or two probably won't matter.
If you cannot do your own repair work, and are not well-stocked with tool, buy new. For $1200 you should be able to get a really nice bike, equivalent in weight and performance to a higher-end ten-year-old bike. The latest Sora and Tiagra groups are quite good---as good as the ten-year-old high-end stuff, and in many cases, better, because the best parts of the old designs trickled down ... and so did the best parts of the new higher-end designs.
Unless you want to buy quality steel and pay more, i'd suggest an Al frame/CF fork or a CF bike ... depending on what you plan to use it for. if you plan to commute with racks and panniers and a fair-sized load, I might worry about the capacity of some CF frames at that price point.
if I had no tools and limited repair skills, I would look at Fuji and Giant and buy as much bike as I could afford and ride it for the next to decades. Which models you would consider would be determined by how you plan to use the bike.
If I was on a tight budget, I would avoid used bikes because pretty much anything used Might need some repair or replacement---tires, tubes and cables at least---and might have minor problems which might get overlooked on the parking-lot test ride. And EBay used ... i guess you are protected by their return policies, but that means waiting on the bike, getting the bike, finding the fatal flaw, reboxing it, taking it to UPS, and after a couple weeks and a couple bucks, have no bike and a lot of disappointment.
On another hand, I got my Cannondale Rize MTB off craigslist and it was ready to ride and in awesome shape and really fairly priced.