I currently use Mobil 1 Synthetic ATF. Previously used Quaker State Dexron III. I notice that shifts are smoother and feel more precise with Mobil 1 especially nearing the 50,000 km (31k mi.) point. Note, however, that Mobil 1 Synthetic ATF is not on the MB approved fluids list but Quaker State is on that list. One of the local MB dealers sells Quaker State Dexron III for the older (pre-722.6) trannies.
MB Approved Dexron III Automatic Transmission Fluids-
Castrol Dexron-III/Mercon ATF F-30341
Castrol Transmax M-22257/22096
Chevron ATF Dexron III F-30108/30159
Citgo Multi-Purpose ATF D-21571
Exxon Superflo ATF Dexron III F-30111
Havoline ATF Mercon/Dexron-III F-30321
Texaco ATF Mercon/Dexron-III F-30321
Pennzoil ATF D-22413/F-30110
Quaker State Dexron-III/Mercon F30161
Sunoco ATF Dexron-III/Mercon F-30176
Unocal Multi-Purpose ATF D-22413/22431
Valvoline ATF Type D
From the Mobil 1 Synthetic ATF product description-
"Mobil 1 Synthetic ATF is recommended for use in modern high performance automobiles, SUVs, SUTs, vans and other light trucks requiring Dexron III and Ford Mercon performance levels."
http://www.mobil.com/Canada-English/Lubes/PDS/iocaenpvlmomobil_1_synthetic_atf.pdf