I’ve been riding my Oracle 36 for 6 years now and I love it every time I get on it. Riding dual hole 150/127 cranks. I’m very rarely ride the 150 hole and really do very minimal off road with this unicycle. If I do, it’s mainly cross-country, fire trails and the like, and I use the one 127 holes. I live in a pretty hilly area and I can get up almost any Hill except perhaps the longest, steepest hill. I’m looking into trying something a bit shorter. I’m thinking the 110/127 or the 117/137. Maybe the 117, as perhaps I could use the extra leverage over the 110s given the hills around me. The 137s give me a bit extra leverage in case I want to do more off-road stuff…but again I rarely do that apart from fire roads… Advice?
I’ve only used 127mm on my 36" and it works for me. The maximum hills I can ride is about 18% but mostly pretty flat riding.
I like this chart:
I am riding 125 also on the oracle. I would be curious to try 117/137 crank but its hard to justify having more cranks than unicycle.
According to your signature, you own a pair of 110/127 mm cranks. I’d try putting them on the 36", and then you can decide wether you would prefer a bit longer ones or not.
I don’t think it’s hard to justify more cranks than unicycles btw. Cranks are a cheap way to change your setup.
Used 125mm on my 36er for an absolute age - this was for commuting, long distance rides, and gravel grinder type not-quite-off-road stuff. For me it’s a brilliant all-rounder.
I’ve also used 114 and 100mm - both are pretty awesome but a lot more limited to more ‘traditional’ road riding (though I can pretty much climb the same on the 114’s as the 125’s if I’m warmed up!)
Also consider that I’m on a Qu-Ax 36er with 48 spokes, a full-thickness 36er butyl tube, and the TA tyre - With a 36 holed Nightrider rim with the new Lite 36er tyre and the lighter Vee tube (or a stretched 29er/blue thingy tube) you’ll probably fare even better with short cranks.
Signature is out of date. No longer have those cranks
Hmm… I just got the Nimbus VCX 100/125/150 cranks as I like short for road (100-120) and not-so-short for off-road (125-150).
In the last months I haven’t ridden as much 36 (wanted to ride yesterday and my tire was flat: my Nightrider tire is finally dead with cracks in the tread and have to order a new one). But in the past 2 years I experimented a lot with crank length.
If you’re somewhat comfortable doing light XC on 125s then I think you will find the jump to 117s on road easy and comfortable. I found the jump to 110s more significant and will fell different and maybe take some getting used to, but for all but walking speed in the pedestrian zone I found it good (I actually found the difference between 100s and 110s less than 110-117).
From your desired description I think 110/127 sounds like a good option, although 117 may be the best for “easy road cruising”.
Here’s my experience with 36er cranks, at least before I got my Schlumpf 36. The rules are different for those.
My major experience with big wheels before I got my own Coker in 2002 was with my handmade Unicycle Factory 45" wheel, which came with 165mm cranks. I have never questioned that size for that wheel, which is kind of heavy, and those cranks are still on there. The uni primarily gets used in parades, where control is more important than speed. It goes plenty fast with the 165s!
I consider the most “versatile” crank length for a 36er to be 125/127. Of course “versatile” has to mean you aren’t climbing mountains or riding technical trails. While some people do pretty well on difficult trails with 125s, they don’t represent most of us.
The vast majority of my 36er riding has been on the American River Bicycle Trail, which is a 33-mile route along the American River from downtown Sacramento all the way to Folsom Lake. This trail is relatively flat, though most of our riding on it in recent years is on the more hilly part, along Lake Natoma and up to Folsom Lake. Basically one big hill, lots of smaller hills, and nothing above 6% grade. Riding there on an ungeared 36" with 125s is kind of sad for me. Enough leverage, but kind of slow.
During 2007-2008 I did a lot of training rides for the Ride The Lobster race. For the bike path, my favorite was 114s (a normal size for square taper, apparently). That still allowed for all of those hills, but upped the speed a bit. When I was really fit, I was also doing it with 110s, but the bigger hills were always a bit of a struggle.
If you know your course will be pretty flat, you can go shorter. My best Marathon race time was done on a borrowed 36, with 102mm cranks. I wanted 110s but nobody had any. It was a struggle on the few small hills along the route, but mostly pretty fast.
What about other rides? For steeper rides, like the annual San Francisco Unicycle Tour, I always used 125s on my ungeared Coker. That ride has about 3000’ of climbing over about 42 miles, and some of it is pretty steep. I also opted for 125s in Ride The Lobster, though I did a lot of my riding on my teammates’ Schlumpf 29er (can’t remember what cranks were on that). I think I’ve also used 125s for the various metric century rides my wife and I have done. None of those were flat either. 
So, based on the OP’s description of terrain, I’d go for the 117s, or the 2-hole 110/127 option for more veratility. If you want even more versatility, the VCX 100/125/150s might be perfect. Road, mixed, and Muni.