I've also always used the NYT calculator, will need to play with both some more when I'm not on a quick snack break but initial observations:
1) if you input the same values into them both, they seem to come up with a similar timeframe for when buying becomes worth it
2) advantage to excel version: I think you can adjust more of the variables than in NYT version (possibly becomes a disadvantage if someone doesn't know what they're doing and puts unrealistic values in I guess)
3) another excel plus: all the income stuff you can include (and the "do you have enough salary for these expenses?" column)
4) advantage to NYT version: fancy graphics make it easier to see what's going on right away for those of us who need extra visual help spotting the most relevant info
Thank you ak907 for taking the time to make it! I'd been meaning to run numbers on this again soon, so now I have 2 handy tools to double check against each other when I do!