I believe its somewhat subjective and differs based on user experience. I have tried transend 8gb cls2, Kingston 4gb cls4 and sandisk 8gb cls4. From MY EXPERIENCE, I feel my sandisk 8gb cls4 gives best performance among the 3. I run Android on sandisk without music stutter.
Also, there are few other threads discussing same topic, perhaps its better if you post your question there as they have more experimental data.
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» HTC Touch HD 2
» ROM: VKVROM (SelfCooked using osKitchen)
» Radio : 2.12.50.02_2