I'd say with a tank the size your considering, get a Sax species, but Johanna's are cool and get nice color on them when mature, just be sure not to get a Venezulan or Stritiga, they get 20 inches plus from what Peanut says.
I currently have a few pikes in one tank, but if you do this, do not get a Lent, from what I hear they are very viscious, on average more then other pike toward each other. Make sure you have lots of hiding places and enjoy. They are awesome, nothing like watching a true freshwater pred roam it's territory. They stare right at you with a crazy curiosity.
I currently have Two Fire Atab's and a Regani, along with two unidentified (to me not to the hobby) Sax species. Love them, and they seem to get along pretty well for now in my 6ft long tank, but the Lub species grow much larger then the others so the others will eventually have to go im sure. That Regani is a looker though, very nice coloring and by far the most aggressive right now, they are all roughly 3.5 to 4.5 inches long.