I have a Mark VI that I have had for 47 years but I play vintage. I find that the older horns have a better sound but you may be hindered by the keywork, mainly the LH pinkies and palm keys. Modern horns mostly have a feel similar to a Mark VI but Conns, Martins, Kings and Bueschers tend to get better fingering as the years progressed. For most people, price will dictate what you get. Examples would be 1920s horns such as Conn Chus, Buescher TTs, Martin Handcrafts which will run you under $1,000 for a good playing horn with a nice finish, mosly plated horns. 1930s saxes like Conn 6Ms, Buescher Aristocrats, King Zephyrs, Martin Committees, may run up to $1,500 for a really nice example. The "primo" horns like a Conn 26M or 28M, King S20, Buescher 400, Martin Comm II, Magna will start around $1,500 and go up depending on condition.
The Mark VII is an overlooked horn that can be found in the $2,000 range and up. Whatever you choose, make sure you can play it first. Look for something local and play it. If that is not possible, get something here at SOTW that can be returned. I have a few Martins for sale in the $800-1,500 for example and every day I see really nice horns in the Marketplace at SOTW that look like good buys. Right now Conn 6Ms are fairly reasonable and Martins are really overlooked and are lower than they have been in a few years. Now is a good time to buy!. Also for the price of a Mark VI, you can get a set of Vintage soprano, Alto, Tenor and Bari OR one each vintage Conn, Martin, King and Buescher Alto......no lie!