If you cross at Nogales it makes sense to go south on Mex 15 to Hermosillo. Mex 15 is not a bad road , getting to be mostly four laned and heavy truck traffic. And a few toll booths too , but nothing to worry about if you make a point of avoiding the one at Magdalena simply by going through the town, not the by-pass; north of Hermosillo about 35km you can turn off east to Pesqueira and take the paved road south and back to Mex 15 /17and Hermosillo so avoiding another toll . Mex 15 is rather straight and fast , leaving the mountain and valley landscape at Santa Ana , then just being flat semi desert ranchland with irrigation farms in spots.. From Hemosillo take Mex 16 east , again fairly flat for the first hour or two but after 160km the serious curves begin. as you start climbing into higher country.Mid Oct. it should be pretty with fall colours starting to turn on the trees and brush.
I would recommend spending the night in Hermosillo, explore the town and go to the outlook point (mirador) atop the small rocky peak with all the radio/TV towers at southeast of the Centro,you can ride the cobblestone spiral street to the top ,watch sunset.. Leave Hermosillo after breakfast and have a nice ride to Cahuizori or Basaseachic for the night, or if you want to stop earlier think of hotels in Yecora especially if it is after 4pm because this section is very curvy and slow and you do not want to be out at night dodging horses and cattle. .
If you enter at Douglas I recommend taking the route Mex 2 east across the mountains into the highplains country at Janos , then south on Mex 10.
Going south from Douglas on Mex 17 is a good paved road and scenic ,agricultural vallies of the Rio Sonora , but you are actually just backtracking to Hermosillo. But if that is what you want to do , nothing wrong with that, the route is interesting.Perhaps you mention taking Mex 17 south because on your one other trip from the ferry from La Paz you came north along Mex 15 and you are now seeking an alternate route to Hermosillo so you can pick up Mex 16 east from there and then take the inland route south from Creel. That sounds like an excellent plan. In my earlier post I dealt with some options on that route.
There really is no need to worry too much about which route is the more scenic, I figure everything you encounter will seem new and different. Do whatever route strikes your fancy, then on next trips you can work on different approaches.Avoid the urge to micro-plan every step of the trip,e.g. making hotel reservations all along the route- very hard , and even if you could this would be a recipe for disaster as you would find it impossible to keep to most of those scheduled, or you'll race along or ride into the night just to keep from losing your deposit. But you say you have ridden in Mexico five times so this should not be news to you. Give yourself lots of time to go slow ,to stop to enjoy the scenery, to explore the small towns, villages, engage the locals in a chat. . If you make your planned goal for the day early resist the urge to go another 100km" just an hour more ", when you barely have an hour of daylight left.Sure enough you will find that the "hour's ride" will turn out to be inadequate to cover the wee distance it seemed on the map.
Further to Lucky Explorer's comments about the ferry service, check out TMC and www.bajaferries.com.mx and www.sanbornsinsurance.com then click on their their ferry info , I think you will find regular service from Topolobampo ( port for Los Mochis) and from Mazatlan. Both companies run several vessels each and accomodations vary. However on the 5 to 6 hour run from Topo getting a cabin is not advised , don't see how you get any adequate sleep in such a short stay even if the sailing time is late at night. From Mazatlan the two of you might want to splurge on a cabin for the 16 hour overnight trip, but you can "rough it" in one of the lounges ' recliner chairs supplied for that purpose.
Lucky Explorer's suggestion for the route from Creel is a good one and would fit nicely into the route to Creel after having come down from Janos. That way you are not returning by way of the same route Mex 16 from Hermosillo except for the segment from Mex 16 down to Creel. On the return from Creel north back to Mex 16 you would be repeating but even then with your bikes you could handle the 85km gravel shortcut west from San Juanito to Basaseachic. This road is excellently laid out and maintained about ready to be paved ( I prefer doing loop rides, with a minimum of re-running the same roads in the same trip) Check out Basaseachic waterfalls from south rim of canyon and from north rim. Mex 16 west from Baseachic will be very curvy and slow going so think of the time/ remaining daylight. Good small hotels can be found en route in Basaseachic/Cahuizori , Yecora on Mex 16 and on Mex 12 south at Rosario ,then in Cd. Obregon where you enter Mex 15 just south of the toll plaza (Travellers from either direction on Mex 15 can avoid it by going through the city and re - entering Mex 15 later- a bit detour but easy and interestring, saves cost of half tank of gas.). Pace yourself.
Alamos is indeed interesting , turned into more of an artist colony and retirement place for the rich.
Decisions,decisions! What will it be via Los Mochis or the long way south via Mazatlan?. Enjoy.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93