Tough call.
I would rate NEET PG slightly easier than NEET UG. The insane competition that NEET UG boasts of is unparalleled. I seriously doubt if I stand a chance at NEET UG if I were an aspirant right now.
The single window approach of NEET UG makes it a tough nut to crack. NEET PG would soon become close with Central Institute exams twice yearly disappearing and NEXT taking over as the single entry for all postgraduate admissions.
NEET PG going clinical and case based with graded questions helping to differentiate candidates viz a viz straight out of NCERT factual NEET UG clearly gives an advantage to NEET PG.
That being said, it is incredibly tough to get into specialities like Radiology or Dermatology in select top Institutes because the seats are inherently too less.