Far FAR more important about "just where" it goes is "just what" it does.
You want the main battery neg ground hooked to the block/ transmission because on startup, THAT is where the heaviest current the car ever uses will be seen---by the starter.
The ground strap from the engine/ transmission to the body/ frame transfers the neg. ground side of the circuit to accessories such as lights, stereo, AS WELL AS tying the voltage regulator CASE (ground) AS CLOSE AS POSSIBLE (in voltage) to battery negative.
The more 'stuff' you have---high current lamps, AC blower, rear defroster, big big stereo, etc, etc, the bigger this ground strap needs to be
ALSO it often helps for radio noise---and in this day and age---this "noise" is also present in ways "you cannot hear" ---that is--- the r.f. noise can affect gauges in newer systems, electronic ignition and E.F.I. and other control systems.
So you may need multiple ground straps from the engine to the frame, and on conventional autos, a couple of sort straps back near the rear of the hood to the firewall.