I personally think the metal route is the most useful, because metal rocks= ingots=metal rods=snails=building materials. Also, you can make metal bars and girders with the ingots, and you could get a lot of money off them. The wood route is another useful route that many people use, as it is a vital ingrediemt for wall segments. Everyone wants wall segments.
I'm in MeRL, Micro Resource Loop. I like it because, well, I like all things micro. What I did was join one route, then I joined the route groups, even for ones I'm not a part of.
When I am in-game, depending on what resource I need, I click on my little face in the top left corner (no need to exit game), scroll down to then click on groups, find the one I want, either Merl or HRR, click on group, read info such as "Minkey = Peat" then click on the name, click on view home street, click on go to home street, close that window, game takes me to their street.
Wow, seems more complicated typing it out! I think it is kind of easy though, in practice. That way, if I don't have a street sign to the place I'd like to go, I can still get there "easily".
Maybe if you go to the groups you can peak at the threads and see who has what, to see if it looks right for you.
I usually regularly post analytics data showing the relative popularity of each resource. Here's some I took just now: imgur.com/a/90dUw. Note that you shouldn't compare the percentages directly, since there are other links on the same page whose numbers are not shown.
I'd imagine that getting involved with anything needed in tower construction should mean plenty of visitors whatever you choose. Plus even if something isn't so popular now, some update might turn things around overnight.
You should join my wall segment route! Towers are a big hit right now, and all our new glitchen are working on expanding their homes. You can find it on the first site M-3tra posted above.