Wally West did it one time by running 13 trillion times the speed of light
In JLA (1997): Issue # 89, Wally West saves half a million people from an exploding nuclear warhead. Below is the image:
JLA (1997) #89
According to the comic, Wally carries 500,000 people 35 miles away from the blast within 0.0001 microseconds.
Although the issue doesn't specify his exact speed, it is evident that we can calculate it from the data in the image above. Also, there have been several calculations on the internet about his speed using these values; one of which is here.
However, almost all of them arrive to the same conclusion:
Wally ran about 13 trillion times the speed of light.
And that, is the fastest one I've seen/read about in the comics.
EDIT: Another feat by Wally was when he outran teleportation in The Flash (1987), Issue #138
Flash [Wally] managed to go the end of the universe and back in under a plank time, which is the time it takes for light to travel a plank length which is 1.6 x 10-35 m or 10-20 times the size of a proton. This is the shortest distance possible, and light can do that in plank time, the smallest measurement of time that has any meaning, and is equal to 10-43 seconds. This is the time it takes for teleportation, Flash beat teleportation and went past trans-time velocity, he traveled to the end of the universe and back under Plank time, i.e., he beat instantaneuos teleportation. He went at at least 23 tretacillion times the speed of light (or 23,000,000,000,000,000,000,000,000,000,000,000,000,000,000). However,
Wally gets all 5 billion people on the planet to agree to run so that he can borrow their kinetic energy and beats the space overlords in record time. Also, he is helped by a fourth-dimension alien species that are pure kinetic energy.
So, you could consider this cheating, from a certain point of view. Nevertheless, Wally did run faster than teleportation.
Couldn't find (as of now) any comic book that specifies Jay Garrick's top speed. However I remember reading somwhere that his maximum speed is 99.99999% the speed of light.
Speaking about the Allens (Barry and Bart), once again I couldn't find any reliable source that mentions their top speed [like it does for Wally].
Sidenote: In the Flash CW series, episode Flashtime enter Flashtime, we see Barry go into flash time just before a nuclear bomb is about to explode. A quick calcuation here says he went at 99.99999999999999982775% the speed of light.