Wally West is my favorite to have donned the title, largely because I’ve read more comics starring him than any other speedster, so I have been able to follow his character arc over time.
Walter West was a fun variant of Wally who operated in the mainstream universe for a year’s publication. John Fox also managed to operate in the present-day era as the Flash for a while, and I like his predominantly blue costume. Avery Ho is one of the coolest speedsters to come out of the last decade, and she handles the title of Flash fairly well. Jesse Quick only got to bear the Flash mantle for a couple issues, and it was largely a ploy to help Bart mature, but I do like Jesse’s character. Sela Allen is unique among Flashes for being an energy being while out performing heroics, and Thondor Allen is goofy, but I love seeing a plus-size Flash. Jace Allen’s costume was a little more lackluster but not abysmal. Lia Nelson (formerly of the Tangent Universe) is someone who used the name for a long time but has a fresh power set.
I prefer Bart as Impulse (or Kid Flash). Jay has my respect for his wisdom. Barry has my respect for his intelligence and integrity.