I like my one piece Roadcrafter but I do wear a Roadcrafter jacket and Darien pants from time to time on certain trips. The one piece is my go to 80% of the time though unless temps are above the mid 80s most of the day.
The one piece is so fast to get into.
The 2 piece is just as fast when used with the elipse combiner zip in...and it also assists when those summer temps climb, as you can have the "option" of removing your jacket when stoped, and getting a slight increase of air flow when the elipse is not zipped in.
After owning a 2 piece foralmost 14 years, I'll add that when you want to wash, and re establish the waterproofing of tyghe surface, the 2 piece fits the washing machine and dryer much easier... I tend to wash the pants 2x more than the jacket, simply because of the road grime on the legs, so its. Great because I don't have to re treat the whole suit to re waterproof.
It also allows for a lot better customizing in sizes, when you want custom ad ins like knee and elbow pad positional dimensions during the manufacture, . And finally, if one section gets damaged, it can be replaced...at a much lower cost...
Just reflecting the benefits I've found over the years, and am glad when I bought my stich, I talked to others that had both, single and 2 piece, to make my specific needs and usage wiser.