I'm not really in favour of having the DRL run underneath multiple transit-carrying streets. That really doesn't help eliminate intense surface transit on either of them, since the service would still need to operate because only part of it would be duplicated. Stick to either King or Queen. The only exception to this would be running on Wellington through the core, since it would be close enough to King but also still be able to easily connect to Union.
The advantage of using King over Queen is that you would intersect the Queen Streetcar at both ends, which would help alleviate the load on the inner section of the line, opening up more room for local riders. Presumably riders coming from South Etobicoke would transfer at Roncesvalles (or wherever the transfer is) instead of crawling along Queen the whole way into the CBD. You'd be effectively increasing the capacity of the Queen streetcar at the same time.
If you use Queen, the only places you intersect the King streetcar are at Broadview and at Roncesvalles, and by that point they haven't picked up much ridership, since they're just starting their routes. The Queen streetcar on the other hand has significant sections of its route that lie west of Roncesvalles and east of Broadview, which generate a significant portion of the ridership.
The advantage of using King over Queen is that you would intersect the Queen Streetcar at both ends, which would help alleviate the load on the inner section of the line, opening up more room for local riders. Presumably riders coming from South Etobicoke would transfer at Roncesvalles (or wherever the transfer is) instead of crawling along Queen the whole way into the CBD. You'd be effectively increasing the capacity of the Queen streetcar at the same time.
If you use Queen, the only places you intersect the King streetcar are at Broadview and at Roncesvalles, and by that point they haven't picked up much ridership, since they're just starting their routes. The Queen streetcar on the other hand has significant sections of its route that lie west of Roncesvalles and east of Broadview, which generate a significant portion of the ridership.