The Tour of course.
Firstly, Giro has only two short ITTs. 23 km is a bit too less.
Secondly, Tour has GC stages all over the race (Rousses and Morzine in the first week, Mende, Ax3 Domaines, Luchon in the second week, Tourmalet and ITT in the final week) while Giro starts with 14th stage only.
Thirdly, Giro has only two hard MTFs in road stages (Terminollo and Zoncolan) and in none of those stages there are 1st. cat or H.C. before the final climb. However, Giro has some serious climbs before the MTF (Mortirolo in Aprica stage and Gavia in Tonale stage) but as experience has shown those climbs might not be very decisive if they are not followed by hard MTF or short decent. TDF has it all - decent MTFs with at least one 1st cat or H.C. just before the final climb.
Fourthly, Giro has Corones ITT but if there is an uphill ITT then there should be long ITT as well. I would rate Giro higher it had long ITT instead of Corones and final stage would have been without short ITT.
Fifthly, Tour has more stages with decent that could provide GC action (Luchon and St.Jean vs Asolo). A climb in Asolo stage is harder than aforementioned TDF stages but it is located 40km before finish while in TDF they are located 30km and 20km before the line (Asolo is single col stage while St.Jean and Luchon are multiple col stages).
Sixtly, medium MTFs of Tour are harder (Rousses and Mende vs Pejo Terme).
Vuelta could also be criticized that there are too many single col MTF stages but it has more ITT kms than in Giro. Vuelta still has some stages with hard MTFs and hard other cols.