Most iced teas are usually "mass-market" brands such as Lipton. Some of the best iced tea powder is sold by Lipton (especially the peach flavour). Understand though that this is a generic powder mix and not really “tea” but really just sugar and a bunch of other “sweeteners” and preservatives.
We at Chai & Mighty will address how to make the best and freshest iced teas:
For the best iced tea, our highly recommend purchasing some high quality loose leaf tea — either black tea, white tea or oolong tea. From there, I would steep the tea leaves based upon the brewing time given in hot water until it is brewed. I would remove the tea strainer (assuming you are using one or using a pot with a removal strainer) and pour the brewed tea into a jug. I would not add iced to the jug but rather place it inside the refrigerator. If you were planning to flavour the tea using lemons, mandarins, plums, hibiscus or rose petals. etc. I would add them to jug (in the desired quantities depending on strength of flavour) before placing inside the refrigerator. In ~2–3 hours, your iced tea should be sufficiently chilled to consume.
Pictured: Glass of peach iced tea using green tea. Source: Pinterest
My top recommendations for loose leaf teas to use when making iced tea:
The White Kanchenjunga: a fabulous white tea from the peaks in Darjeeling.
The Earl's Black Jack: A rare blend of our favourite black tea (given below) and a classic Earl Grey.
The Darjeeling Black Jack: A smooth black tea with a chestnut-red hue, it makes a fantastic iced tea (using its third brew!)