Depends how you want ot classify it, but if you mean bumpiest then I would say the flight I did from the island of Islay back to Glasgow with 3 passengers in a Cessna 310 a couple of years back.
It was forecast as 'severe turbulence below 6000' in the Scottish FIR' and they were right. It was howling but steady just about down the runway at both airports. I briefed the passengers before we even boarded that it was going to be very unpleasant but safe enough knowing the limitations of the aircraft and my abilities. The decision was theirs as to whether they wanted to go or not(I had already decided that I was willing to go) and they decided they had to get back to connect with the BA shuttle to London that afternoon.
We took off after about a 200m roll the wind was so strong and as soon as we were airborne the bumps started. We were only climbing to something like 5000' so we were in it all the way, really being flung around. We hit a 'hole' and dropped a couple of hundred feet at one point and were 'airborne' inside the cabin, only being held down my our seatbelts which were being tightened more and more!!!
I smelt sick as I turned onto the localiser at Glasgow and hoped that it had made it into a bag as single crew ops usually extends to cleaning up the mess.............
We landed long and still made the intersection turn off! G/S was about 40kts coming over the numbers!
Fun, I miss it.
PP