Rainforest
When the TC lines were announced, I thought of the hydro corridor as the obviously preferred location for Finch W LRT. But all factors taken into account, this is not so obvious. Hydro corridor might be more trouble than it is worth for this route.
First of all, the speed will depend mostly on the stop spacing and the implementation of traffic signal priority, rather than on the alignment. If the line is in hydro corridor, it will stop anyway at all major concessions (Bathurst, Dufferin, Keele etc) and at mid-concessions (such as Senlac, Alness). In principle, same stop frequency can be set on the street-ROW line; and if the traffic signals allow the transit vehicle to breeze through other (minor) intersections, it will be as fast as in hydro corridor. In reality, the stop frequency might be set higher on the street-ROW line, but that is a matter of choice rather than technical limitation. And even then, the difference is not likely to be large.
Then, construction in the hydro corridor might seem cheaper, but there would be a number of hurdles to overcome. Yonge to Bathurst, it might be too close to the residential backyards. Bathurst to Dufferin, the Lord Ross Reservoir needs to be bridged or bypassed, soccer fields would have to be closed, and some trip generators (plaza at Finch / Bathurst, apartment buildings near Wilmington) would be missed. Dufferin to Keele, LRT tracks would have to be built into the planned York U busway. That requires coordination between the two TTC's projects, something the TTC does not particularly excel at. Around Jane, the street alignment is preferred, to better serve the large shopping malls.
Perhaps the LRT belongs to the on-steert ROW, while the hydro corridor should be reserved for some future, truly express, inter-regional service. The latter could be an inter-regional busway, or LRT express tracks, or REX rail.