Most Constantly Visible: My citron goby is always up front and accounted for, clinging to the side of the tank glass or in the middle of the central gorgonian in the tank. He fears nothing and, at two inches in length, bright yellow w/ a massive (for his frame) skull, he really sticks out, even in a 56 gallon collumn.
I think my next most visible fish would be the "active peckers." Those fish that need to buzz about, examining rock, which includes my spotted mandarin pair and my Valentini toby. They might be behind a coral for a few seconds, but they really bring attention to themselves by their activity and "take no crap" attitude.
I have three different tanks w/ single clown fish in them (2 w/ ocellaris, 1 w/ orange skunk), and none of them are "fore-front" fish.