Using a sawzall is probably your best bet, certainly the fastest way to knock it out. If you want to actually remove the posts you need to get a hose and soak the area around the post (water the post like a thirsty plant). once it gets really wet use a post puller (you can pick one up for $30-40) and a lot of muscle. Honestly I removed the chain link fence at my building and my neighbors and I pilled out probably a dozen posts with the concrete and then I just flush cut the posts and a few years later you can't really tell the difference.