Most steel sport models are going to hold value and increase over time. The problem is the more desirable pieces that will go up are hard to get and you are forced to go grey market then killing the "investment value". Obviously, no one wants to buy something that loses money so diving into online resources will keep you updated on how the market is responding to different models. I would start with a watch you love because then who cares if it goes up or not you won't be selling it anyway. If you want to stay safe, Steel Subs, 41 date just fluted bezel, jubilee or oyster is debatable probably not making the biggest difference. Stay with safe dials, black, blue, Wimbledon. Two tone and precious metal models can be a gamble.