I have stayed at the Tuscany once and it was fine. The latest reviews seem pretty good. I have visited this property many times and it seems fine. I love their TV / Radio commercials - "Meet me at the Tuscany!" They cater to locals.
If you can save a few bucks - go for the Tuscany. Remember it is spread out in many Motel style buildings, but you have a rental car - so that should not be a problem. Also, look for buy one - get one offers for dining at the Tuscany on the internet and in local newspapers (LVRJ, The Sunday, Vegas SEVEN, and The Weekly). I do not know if the online versions have the same coupons as the print versions.
I have never stayed or visited the Candlewood Suites.
Good luck on your choice and enjoy your visit to LAS. Safe and happy travels!