I don't have much experience with it yet, but I'm most interested in the miniature varieties. They mature quickly and can be grown with close spacing.

I also agree with Simpson Elite as a fantastic lettuce for hydro.

I also grow a steady supply of a mesclun blend. I am unsure of each particular variety, but I separate the seeds before germination and grow several of each type.

You may recognize some of the varieties in this picture.

Here is a link that might be useful: Video: Indoor Lettuce Harvest

What did you decide?

Thanks halfway, I also agree with you that Simpson Elite is a extraordinary lettuce for hydroponics system.

While this is an older post, I thought I ask anyway, in case you are still watching. Have you tried Bok Choy? You mention 'without using a greenhouse', so I'm assuming your setup is outside, not in a controlled environment - basement with lighting, etc... either? I'm pretty new to all this, but I believe Bok Choy does well in a hydro setup, and personally I like the mixture of textures it has - really crisp stalk, and then the greens that are a bit wimpy when it comes to crispness. Combine them with some corn, some beets and some bell peppers, and you've got a good variety of textures to start with on the veggie side.