It's likely you will get a different opinion from each owner with a different configuration.
When we ordered our boat from the factory, Jeff asked how we intended to use the boat and then recommended the Honda 135 for us. I've had many folks ask if it's enough power... and it is for the way we cruise. At the time, I didn't want two 90s on the back, because Honda didn't offer electronic fuel injection on the 90s. Certainly, the twins on the back give you some redundancy, but you will also have twice the maintenance and expense. The only time I have wished for more horsepower has been at higher elevations (like Lake Tahoe, Yellowstone Lake, or even Lake Powell); most of our cruising has been at sea level.
The only time we are not heavily loaded is when we're home for a while and just day-tripping. The Honda 135 has been a good match for our cruising style.
There is a good Honda service place in our area, and that was a factor for us, too. I've had other Hondas and (with the exception of a cranky Honda 5 we bought for a dinghy) they've been quiet, dependable, and fuel efficient. I think all the major engine manufacturers make good motors, so it's more a matter of what you want, what service is available locally, and what your dealer offers (assuming you're buying new - If you buy used, you get what the previous owner wanted).
Single or twins? Yep, they both work. As far as docking, the twins on a 25 are so close together that you don't gain much of an advantage for differential power in maneuvering. There is quite a bit of windage on these boats, but practice will improve one's technique. Oh, and good fenders.
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Your questions here bring up an interesting perspective. It seems like many owners here come from sailing backgrounds, open fishing boats, or even downsizing from bigger trawlers. It would be interesting to hear from owners who moved to a C-Dory from (what I consider) more modern looking (what some call "bubble boats") cruisers with a cabin below. Can someone here give Duff a "been there, bought that" perspective?
Good luck with the search and decisions.
Best wishes,
Jim B.