Taste is subjective to each individual's palate. At times we get conflicting views from different people as to the sweetness of our lettuce. But then some lettuce (endives) are supposed to be bitter in taste.
Common feedback from the Jaya Jusco and Cold Storage supermarkets from public food tasting sessions is that our butter lettuce and romaine lettuce is much sweeter than alternative supplies.
Several factors affect taste in vegetables (commonly judged by the sweetness factor) such as: age of plant, sunshine levels prior to harvest, temperature, particular variety of that vegetable, harvest and post harvest handling conditions.
In conclusion it is very difficult to state that hydroponic or non-hydroponic vegetables have a different taste by virtue of the growing medium alone.