Two positives with the RCI connection - two potential negatives. First the RCI option is a good one. It creates one additional option for exchange that most Marriott owners aren't lucky enough to have. Because of that relatively low amount of deposits they carry a high exchange value (big demand, low supply in that system). Second RCI will accept ONLY what you own for deposit. No games of substituting a similar week. You get to deposit exactly what you purchased/owned. Ask Wastegate owners how important THAT is. Wastegate also went down the path of substituting lesser weeks for deposit to II rather than the deeded time actually due to the owner. It is so sad to Marriott now sinking to that lowlife action.
The downsides have to be considered as well. You pay to be an RCI member (not so bad if you have other weeks in RCI as one fee covers them all) but you can drop your II fees so that makes up for a good portion of that fee. Plus there is the extremely member unfriendly court finding that allows RCI to rent owner deposits for TRADE to be redirected to rentals after a very short window of trade only being allowed. That has really ruined the RCI Weeks system as a long term option unless you don't mind that the best times may be siphoned off to rentals after only 30 days. Move quickly if you use RCI to get the best trades - wait a few days to claim a trade & it may be gone to rental.
Overall, for now, RCI may be the superior choice for those Marriott resorts that can be used there.