I believe with all the present connections and future potential connections to be made at places like Kipling, Mount Dennis, Dundas West, Caledonia, Downsview Park, Oriole (which is like 200m from Leslie Subway station on the Sheppard line), Agincourt & Danforth-Main, and even Long Branch & Guildwood (with an Eg East-Morningside LRT), Toronto & indeed the entire GTA would greatly benefit from a dramatic increase in 2WAD Go trains to at least every hour on every line, not just a Go Rex plan or a DRL. These nodes could be developed into major destination and transfer hubs. I know Metrolinx has identified some of these already but need to get more aggressive about pushing these areas of development further and faster and upping train service to match. Along with true fare & service integration with TTC local services, instead of the ad hoc solutions beginning to percolate now (like Danforth in the east & King in the west). Within a 3-5 year window, a strong push in this direction could yield great results with a full transformation of the wider GTA region's and Toronto's transportation picture within a decade.
With all that being said, the DRL serving a slightly different purpose than the Go network, is, I think, a necessary next step for the TTC. The rail corridors are great but looking at the big picture, there's a gap into which a DRL alignment from Don Mills & Eglinton down to at least St. Andrew (King) or Osgoode (Queen) could slide very nicely.
I believe this shouldn't be about choice as we need both of these major projects badly ASAP.