Also, for what it's worth, when it is not busy and you get a runway assignment you can ask for the other one and they usually give it to you. Some Friday mornings flying in I have been asked what runway I want. When it is busy those luxuries go away.
Please, DON'T ASK. Keep yer dang mouth shut like the NOTAM says - If traffic is light enough, Fisk ATC will *ask* you which runway you want. If they don't ask, don't send them further down the tubes by jumping in and asking them to change their plan and clogging their frequency.
What runway do you prefer / would you ask for if had the chance?
Depends where you're parking. North 40, you want 9/27. Vintage, South 40 you'll want 18/36. Homebuilts and Warbirds, either way works but you'll probably spend less time taxiing on the grass from 18/36.
That said, 36 L or R being a left hand turn from Fisk Ave looks to be the easiest. But maybe actual experience might trump my never been there guess.
In terms of landing, I would rank them as follows:
Easiest is
9, it's just about a 30-degree (maybe less) dogleg from the railroad tracks to final.
Next easiest is
36L, which is just a left base.
Next would be
36R, which is also a left base but you'll need to be good at keeping your speed up after landing, as this is the only runway that you don't jump off into the grass - You just taxi all the way to the north end, and if there's someone landing behind you, you need to not be in their way. On the relatively rare occasions I get this, I fly the approach at 90 knots, pull power on short final, let it float a bit if necessary, and then just use aero braking only - Stay off the wheel brakes until you actually need to slow down at the end.
Next would be
27. This is a right-hand traffic pattern, and you need to be ready to modify your approach at the very last minute according to ATC instructions. For example, when the guy in front of me didn't understand how to make a short approach to a dot and instead wanted to fly his base dang near over the Lake Winnebago shoreline and have a mile final, ATC had a couple of us cut inside him and make short approaches to green and orange dots. Betcha know who got thanked and welcomed to OSH and who didn't.

And finally,
18R is the hardest. This is left traffic to a spot on the runway with a VERY early descent (starting at the crosswind-to-downwind turn), absolutely no flying north of the control tower so you don't get tangled up with 9/27 traffic, and there really is no final - Ideally your base leg starts at maybe 200 AGL and you start your turn to "final" at 50 AGL, complete the turn, flare and land. This is not how most people fly on a normal day.
That said - IMO you should either prepare and practice flying approaches in the style of all of the above so that you're proficient in ALL of them, or you shouldn't fly into Oshkosh - Go to Fond du Lac, Appleton, Green Bay, Brennand, or any of the other numerous airports in the area that offer ground transportation to Oshkosh. You're flying into the busiest airport in the world, so you'd best be on top of your game.
You should be able to arrive and depart Osh and never say a single word on the radio.
FTFY.
I'm probably the only one here who's landed on 18 from the downwind for 27. It was an interesting audible by the tower and a "You want me to what??.. OK" from me.
That actually used to be one of the published approaches, 2018 was the last year it existed in the NOTAM. That said, I only ever saw it get used for the Ford Trimotors, because they're giving rides and coming in on an unpublished arrival from the north, but they load up near 18/36. It would make the list above maybe not as the hardest, but as the most fraught with peril - You'll be even closer to other traffic that isn't on the same frequency, you had to cross the 9/27 centerline at or above 1500' to avoid tangling with go-arounds from 9/27... It was probably the least safe approach out of them all.