Both guys seem to have done ok @ the AHL lvl, and gotten some NHL time.
1. Which guy will play consistently @ the NHL lvl and produce first?
2. Which guy will be the better long-term player?
Don't follow Kalus so I can't say for him. Kostitsyn has to play in the NHL next year as he won't make it through waivers. He has been one of Hamilton's top players and until the last game he was leading the team in points per game, so I got to think he will be back in the NHL this year as injuries will likely hit at some point.
Personally I think Kostitsyn can produce in the NHL right now, but one of the biggest knocks on him that remains is his lack of consistency. He just doesn't seem to want to work hard on a regular basis (which he has improved on this since being sent down after a 4 game callup last month)
I don't know who will be the better long term player but I have my doubts about Kostitsyn at least being a Hab since he isnt' a hard worker and I don't think it will fly with a team run by Gainey, Carbo, Jarvis, Muller. That said he has a good shot and really good passer, got to think he could be a decent 2nd liner someday as he's still only 21 so he has a few more years to develop.