The 2017 MLB World Series was one for the ages and congratulations to the Houston Astros for winning its first World Series in franchise history. The question is immediately brought up when someone wins a championship, can they repeat again next season?
It is quite possible the Houston Astros can win it all again next year, but it will be tough to repeat with teams getting better year in and year out.
Here are the teams that can challenge for the trophy next season!

Cleveland Indians

The Indians had one of the best pitching rotations in the MLB this past season. Terry Francona is an excellent manager. Jose Rameriz emerged into a star this season for the Indians. The next star on the rise for the Indians is catcher Francisco Mejia. Cleveland has ended the season with disappointment the past two years.
They also won 22 straight games during the regular season which happened to be a new American League record. It is very important they bring back Jay Bruce and keep Edwin Encarnacion around.
New York Yankees

The Yankees were one win away from the World Series. They came back from an 0-2 deficit against the Cleveland Indians in the ALDS. Aaron Judge, Greg Bird, and Gary Sanchez is going to be new Yankees core for the next decade if they can stay healthy.
The Yankees need to find a way to upgrade the starting rotation. They also need to find the right manager. 2017 was supposed to be a rebuilding year for the Yankees and they are ahead of schedule. The future looks bright for them.
Los Angeles Dodgers

Clayton Kershaw is one of the best pitchers in the MLB. He will have another outstanding regular season in 2018 and Kershaw will be one of the main reasons why they get back in this position. Young players like Yasiel Puig, Cody Bellinger, Corey Seager, and Chris Taylor will learn from this and be stronger than ever once again.
The bullpen was very good, but they need to find a legit number two starter. Yu Darvish wasn't the answer. The Dodgers will continue to play for one another and they are well managed by Dave Roberts.
Chicago Cubs

The Cubs have an explosive offense with Anthony Rizzo, Javier Baez, Anthony Rizzo, Jason Heyward, Ben Zobrist, and Kyle Schwarber. Ian Happ will be a star on the rise. Chicago had issues with pitching this season. If they can't get Jake Arrieta resigned, the Cubs will have to look elsewhere.
Chicago has made it to the playoffs in the past three seasons. The Cubs are fortunate they play in a division that isn't very strong. That could be a problem when they have to play the upper echelon of teams next season.
Boston Red Sox

They have an explosive offense with Mooke Betts, Jackie Bradley Jr., and Xander Bogaerts. Boston has a potential superstar in third baseman Rafael Devers. If he continues to produce, the Red Sox might be a different team next season. The major question is, can the pitching step up when it actually matters?
The problem was the Red Sox lost to two betters teams in the last two postseasons (2016 Cleveland Indians and 2017 Houston Astros). John Farrell isn't being brought back as manager and Alex Cora will be the new manager.
Washington Nationals

Dusty Baker won't be back in 2018 and Dave Martinez will be the new Nationals manager. He was the bench coach with the Chicago Cubs the past couple of seasons. The Nationals have talent with Daniel Murphy, Bryce Harper, and Anthony Rendon, but they seem to falter when the stakes are high.
Max Scherzer and Stephen Strasburg is a solid 1-2 punch in the rotation. The bullpen is an issue though and they have failed to get past the first round in the past two seasons. Washington game five at home in back-to-back seasons. (Los Angeles Dodgers 2016 and Chicago Cubs 2017).
New York Mets

If their starting rotation is healthy, they can be one of the best in baseball and that is why they made it to the World Series in 2015. Mickey Callaway will be the new Mets manager and they will have high expectations in 2018 after a disappointing 2017 season. Michael Conforto, Amed Rosario, and Yoenis Cespedes will be the main players in the lineup. They need another key bat in the lineup.
The New York Mets got rid of trainer Ray Rameriz and he did a poor job of handling the New York Mets injuries. New York needs to stay healthy during the 2018 season in order to compete.
St. Louis Cardinals

The Cardinals had a lot of injuries in 2017, but if they can stay healthy, the Cardinals will be dangerous in 2018. St. Louis does a good job of replacing players in the lineup because it has a strong farm system.
They have a next man up mentality and that can you help win a night-to-night basis. The Cardinals can have a very good pitching rotation in 2018 if it stays healthy. Matt Carpenter, Yadier Molina, and Stephen Piscotty are the nucleus of this Cardinals team. They usually don't miss the playoffs in back-to-back seasons.
Houston Astros

Alex Bregman, Justin Verlander, Dallas Keuchel, Jose Altuve, George Springer, and Carlos Correra will all be back next season for the Houston Astros. The Astros are well managed, but the American League won't be an easy league to win in 2018.
The Astros are going to have to address the bullpen in the offseason because it was shaky all season long. Ken Giles lost his closer's role during the World Series, but I expect him to regain it during the 2018 season.
Houston has some more young players waiting to prove themselves like Derek Fisher and Kyle Tucker.