The 2017 NHL Draft saw a number of great players be selected in that class including Nico Hischier, Miro Heiskanen, and Cale Makar in just the first five picks. The Buffalo Sabres, unfortunately, were just outside that with the seventh overall pick, so they didn't have a chance at those players and would end up picking Casey Mittelstadt.
Mittlestadt would play seven seasons with the Sabres and had a career-high of 59 points in his final full season with the team. However, even with that one season he never really lived up to expectations and has been traded during the season in consecutive years after Buffalo traded him to the Colorado Avalanche and Colorado would trade him to Boston the following year.
While the Sabres didn't have the chance to draft any of those players previously mentioned, there were several players selected after Buffalo's pick that they wish they could go back and select.
Martin Necas
Martin Necas was selected about five picks after Mittelstadt after the Carolina Hurricanes selected him 12th overall. The two players have played about the same number of NHL games, but Necas has been much more productive with 124 goals (43 more than Mittelstadt) and 202 assists (47 more than Mittelstadt).
Necas switched teams last season after the Hurricanes traded him as a key part of the package to the Colorado Avalanche for Mikko Rantanen. It will be interesting to see if Necas can continue to have the same success he did with the Hurricanes in a full season with the Avalanche. If he does, it will only make the Sabres' pick look even worse.
Nick Suzuki
One pick after Necas is the next player on this list in Nick Suzuki, who was selected 13th overall by the Vegas Golden Knights. However, he didn't play a single minute as he was traded to the Montreal Canadiens for Max Pacioretty.
Suzuki made a big impact on the Canadiens as he would be a full-time NHL player one year after that trade and has been a key part of Montreal's team ever since. He has steadily improved every season to a career-best 89 points this past season.
Robert Thomas
A few picks later in the first round, the St. Louis Blues selected Robert Thomas 20th overall, and unlike the other players so far on this list, Thomas has not been traded. The Blues have benefited the most from their first-round pick, as Thomas has been a key contributor almost immediately and has the most NHL games of any of the other players with 466.
Thomas has already surpassed 100 career goals with 107 so far but has been one of the best in the entire draft class in terms of assists. Thomas' career total of 289 is the second-highest and behind only Cale Makar, who has 312.
There is no question that the Buffalo Sabres could benefit from a facilitator like Thomas in the middle of the ice, and he would have been a better fit over Casey Mittelstadt.