Added some specifics to aid in the decision.
Let's say you are going to join a shared-ownership club down at your local airport. Assume the club has one DA40 equipped with a Garmin G1000 that is rented "dry." Also assume that the club intends to add a DA20 in the future.
Would you rather a) pay high monthly dues (~$150) and a lower hourly dry rate (~$70) or b) low monthly dues (~$60) and a higher hourly dry rate (~$100)?
Years ago I read this:
"To every complicated problem there is a simple answer, usually wrong."
Looking solely at airplane rates and monthly dues could lead you into a very unhappy situation. You really have to look at the club's finances in much more detail. If the club is any size, their tax return/IRS form 990 should be available at guidestar.org. Registration is free, the tax return is free, and there are no negative consequences to registering.
Regardless of whether you get the 990 or not, ask to see the club financials for the past two or three years. If you don't know how to read the documents, find a friend who does.
The biggest wild card is "assessments." For example, if the club does not have a cash reserve or bank borrowing power, when that $25,000 engine replacement comes along are you going to get an assessment for your share? What about that DA20? Will you get an assessment for your share of the down payment or of the full airplane cost?
Another wild card is "who is getting paid?" I know of one medium-sized club in our area where no one lifts a finger without getting paid. The president of the club has been president since Wilbur and Orville walked the earth and he gets a nice part-time income from the club. So does the treasurer, maintenance officer, etc.
Third wild card is yours. From years of involvement in club management I will predict that after the initial "honeymoon" you will fly less than you expect. Are there minimum flying charges? I have never seen a new member indicate concern over this, but 90% of them end up paying minimum flying at some point and some pay regularly. Even if there are no minimum flying charges, do your math for the case where you fly half as much as you expect.
A little bit about flight rates vs dues. The Right Way to set these is to have the flying rates cover the variable costs of flying (principally maintenance but not annuals) and the dues cover fixed costs like insurance, hangar, annuals, etc. Setting things up like this makes the club highly resistant to financial problems caused by flying being below plan. So if you find a club whose rates and dues are wildly out of line with others, you had better start asking questions.
Finally: There is no magic. In the long run everyone's costs (other than paid staff) for similar fleets are about the same. Newer airplanes might cost less for maintenance for a while anyway, but what about problems with those expensive glass panels? If it looks too good to be true ...
So no, it's not just a simple math question unless it is a non-equity club where you are protected from assessments and can walk away at no cost if things get too financially exciting.