Smallmouths get big enough but not quite as large as largemouths, at least in length. Its just a more athletic fish, more svelte. I wouldn't say you need a bigger tank but my guess is that you could find easily find 100 people to disagree with that. All of mine were released at a private pond before they reached full size, the largemouths (about 12 in.) because they were sort of boring/lazy and they crapped so much, and reluctantly, the smallmouth (about 11in.) because I went a different way with my stock. In my opinion, they are similar enough in size that you wouldn't feel you needed a bigger fish if you went with the smallie, and they are way more interesting to watch. Also, if to further show my bias, I think they are way cooler looking. The undertones of the body are darker as well as the markings on the face. (mine varied from a goldish to brown with army green and looked awesome). Lastly, get them on floating pellets and watch them smash the top of the water like they need to kill them, it's probably the best part of owning one.