I think these 2 teams are at a very similar part of their rebuilds even though buffalo's has taken much longer. So which team has the brightest future?

Buffalo and I dont think its particularly close.

Buffalo has outperformed Ottawa this year and has a top 5 Prospect pool in the league still. While Ottawa is towards 20 or worse imo. Now I think Ottawa is in a decent position for a few years, but I think Buffalo's success will sustain longer.

Buffalo's window is looking like 9 years
Ottawa's window is looking like 5 years

Red Wings clears both.