There's lots of threads in this forum about different rides in Tahoe, I'd search those out.
But it all depends on how many days you are riding and how much you want to drive. Downieville is an hour+ from Truckee, as is South Lake Tahoe (Toad's).
Another factor is how much climbing your crew can do at altitude.
Reno is pretty hot in the summer (90F+ most days), and there's much better trails in Tahoe area, so no need to go there.
The basic Toad's ride as a shuttle is pretty short (though a 4 mile climb), so you may want to plan multiple laps or other shuttles that day (such as Armstrong Connector-Corral). Personally, following leaguerider's suggestions, a great way to do Toads is to climb Armstrong to the Tahoe Rim Trail, and follow that to Mr. Toads (once the snow melts).
Lots of fun scenic riding on and around the Tahoe Rim Trail near Tahoe City, including the newish Big Chief trail.
DirtGypsy in Truckee can shuttle you to various spots in North Tahoe -- but you need to make plans with them in advance, as their "scheduled" shuttles don't always run.
Also check the Over the Edge Tahoe website for trail info and shuttles in South Lake Tahoe.