Hallertau is good. I suppose you would want a dual-purpose hop since you only want to use one. Tettnanger is one I really liked a lot, perhaps that is a good one to use but it is really up to you. I think Tettnanger would work well in your previously brewed beers just looking at what you've brewed. I think Tettnanger comes in both American and German varieties as well and I think you'd want German but I am not 100% sure.