Welcome Pickups transfer to TulumorKiwitaxi transfer to Cancún?

The short answer

These do not go to the same place, so price is not the comparison. The Kiwitaxi transfer to Cancún reaches Downtown Cancún (El Centro), where the ADO bus ends; the Welcome Pickups transfer to Tulum does not. Goes south to Tulum, not into Cancún.

The Kiwitaxi transfer to Cancún is quicker: 24 min against 1 h 30.

Welcome Pickups transfer to Tulum: Runs all night. Kiwitaxi transfer to Cancún: hours not recorded.

Priced against each other

Whole-party totals · adult fares

What each costs for the whole party, in MXN. The cheaper of the two is marked on every row. The Welcome Pickups transfer to Tulum is charged in euros; its column is converted at the reference rate in its fare note. The Kiwitaxi transfer to Cancún is charged in euros; its column is converted at the reference rate in its fare note.
Travelers	Welcome Pickups transfer to Tulum	Kiwitaxi transfer to Cancún	Difference
1	about MX$2,455	about MX$792	MX$1,663
2	about MX$2,455	about MX$792	MX$1,663
3	about MX$2,455	about MX$792	MX$1,663
4	about MX$2,772	about MX$792	MX$1,980
5	about MX$2,772	about MX$792	MX$1,980
6	about MX$2,772	about MX$792	MX$1,980
7	about MX$2,772	about MX$792	MX$1,980
8	about MX$3,148	about MX$1,584	MX$1,564