Hell, take a screenshot once with Vanilla, once with mod A, and once with mod B. Look at the same view with the different ENB mod working. Then exit, turn off mod A, install and activate mod B, start Skyrim and load that same save point. Then install and activate mod A, start the game and see how it looks. Just download them both, go into your game, find a nice scenic shot and save your game at that spot. Even other people will be running mods you don't know about, and that might affect their advice. Those screenshots might have been taken with a setup that includes other mods that affect visuals, you might be biased by a particularly well-shot screenshot, etc.
My suggestion would be to not just go by the screenshots or even other people's advice. So if you're using an ENB mod which one did you choose and why? And if you've used a different one before, why did you change to your current one? I suppose it's a lot about personal preference, but it wouldn't hurt to hear other people's opinions.
I like what I see in screenshots from these and they both appear to be updated frequently. I've been going through a whole bunch of ENB mods (without actually installing them to keep my installation clean) and I've pretty much narrowed it down to two options:
