It depends on what you will be using it for. I would suggest the TK41 just because it is brighter, if you need it, and it has a larger hotspot. But if the amount of batteries is an issue for you then follow the above suggestion get the TK50 and get some d spacers with some eneloops. That way you only use two batteries at a time and you still get a bright light. Keep in mind though that the smaller batteries will give you a shorter run time and with the TK50 you won't be able to see as much of what you are lighting up. Out of the two I would say the TK41 is the better light. But, the question is, is it worth the extra money to you?
The TK50, TK41, and TK60 all have the same electronic switch so alkalines are not a god idea in any of them.