I brought some frozen onions from Morrisons when I made some French Onion soup as I couldn't be arsed crying for a week as I did last time, when I used fresh ones! There wasn't any difference in taste I have to say. I have just made a Carrot soup today and added a potato to it which has completely taken out the sweetness of the carrots. Meh!
When our kid was at catering college he was telling me that frozen veg is better than Supermarket fresh as its picked, cleaned and frozen really really quickly, whereas fresh veg can sit about for days, as its moved around the country.
I can attest to that as I've worked on the fridges, for Tesco, Iceland, Somerfields (now Co-op), Farmfoods and a company in Rainford. Last year for example I took a load of fresh veg up to the Aldi RDC in Bathgate outside Edinburgh, it was picked on a farm in Essex, no idea how long it sat in the fridges there, it then got driven to Rainford, went into the Fridge there, put in another trailer which I then took to Aldi, it then goes in their fridge until its picked and sent in their wagon to the store. So even in that example, best case scenario is if it was picked on the Friday, the earliest it got to a store was Sunday night, but more likely Monday.