Here my list of my favorite Sinnoh Pokemon
1-Riolu and Lucario(one of the most iconic Pokemon I love their design and Lucario is very useful Also Lucario is my second favorite Pokemon of all time)
2-Chimchar and Infernape(The best Sinnoh starter their typing are really great and their design are cool)
3-Gible line(One of the best pseudo Legendary, Garchomp is badass)
4-Luxray(A very underrated electric type, Luxray design is so cool)
5-Weavile(Great typing and Design)
6-Roserade(A beautiful Pokemon, it's really useful)
7-Spiritomb(Very cool typing and Design)
8-Pachirisu(One of my favorite Pikachu clone it's so cute)
9-Creation Trio(Their design are great and their typing are really good)
10-Piplup line(Another sinnoh starter that I like, Their design and Empoleon type is good)
Honorable mention would be: Turtwig line, Cranidos line, Mismagius, Honckrow, Gliscor, Staraptor, Gastrodon, Magnezone, Abomasnow and Darkrai.