I own my weeks to use them, but when scheduling conflicts have made that impossible, MyResortNetwork has consistently produced (for me, anyhow) the most genuine inquiries resulting in a rental. RedWeek has never actually produced a renter for me but oddly, despite their "access by members only" model, I still got contacted by a fair number of third party agencies and assorted "tire kickers" responding to ads on that site.I have had some success with redweek & the market place here on tug. My resort network didn't work for me at all, nor did vtr. The problem I find with redweek is that most of the inquiries seem to be about dates other than what I have advertised, even if I post that these are the only dates I have available.
It's only my second full year renting and selling timeshares, so my experience is limited, but all my success has been from myresortnetwork.com. I advertised in both redweek.com and myresortnetwork.com using same descriptions and price. Since all my rentals and one sale have come from myresortnetwork, I'll be giving up on redweek. I have recently tried using vacationtimesharerentals (it's free) and so far received one inquiry.
The absolute key to success in my opinion is to realistically price your weeks.