I'd probably keep the nincada for right now because you can get a Ninjask later. Combusken is a definite keep, although you don't really need Makuhita because Combusken is part fighting. You should probably get something better than a Whismur, because it is quite lacking in many aspects. It would also help to know which areas you have access to just so I can help you find which pokrmon to catch.
Hope this helps.