pesonally speaking, use putra mahkota is nearer. but difference maybe only 4-5km .
direction :
nilai toll : after exit toll plaza then take 1st left at T junction (if take right heading to KLIA/sepang). then come one more T junction, take left again. you will come to Arab Malaysia Industrial park signboard. take left. after about 5km, Nilai 3 is located on the left. can see many cars enter/exit the junction uphill.
putra mahkota : after exit toll, turn right at X junction into bandar bukit mahkota (if turn left go to bandar seri putra, straight to bangi lama). dont bother with security. he he action only.:D as u reach 1st T junction, take right. can also take left, you will come to same meeting point but longer distance.
find a junction heading RH also got ont more security point. this is the border of selangor and negri sembilan. after this point u r in Arab Malaysia Industrial Park. another 5km take RH junction into Nilai 3.
its quite tricky for first timers. i strongly suggest this place as ZTH meeting point.. easy access from highway. close to sepang circuit. got place for yumcha. but not so many young girls around....that's too bad.