About 30 seconds or so seems ideal for green tea.
I've been drinking green tea heavily for four or five years now, after my mother recommended it as a healthy drink. I found green teas work much better unsweetened than black tea, or any other caffeinated drink. During that time I've tried quite a number of brands and flavors, most of which I quite like.
When I first started I brewed it till the tea was nice and dark, so it looked thick, since I've always liked my hot chocolate rich and thick, and the little coffee I drink is loaded with sugar and milk. But then the green tea tasted bad, and I slugged it down because it was supposed to be healthy.
Eventually, I came to realize that less brewing time was better. Most packages say 2-3 minutes, but in my experience that's way, way too long. Less than a minute and an unflavored green tea will have a pleasant, grassy flavor.
The worst is the one I drink the most of, Golden Tips pure Darjeeling, which is the only one here that comes in bargain boxes of 100 teabags. I begin most work days with two cups of this one, and then maybe a couple more during the day. However, I rarely drink it at home...
Brewing for more than a minute or two and it's bitter, sometimes even giving me a nauseas stomach ache. In fact, all of the women I've known who've tried it have gotten really sick from it. Leena tried it when I was in the U.K. and thought for sure she was going to die after drinking it.
Ah, but brew it for about 30 seconds, the time it takes me to walk from the office hot water dispenser back to my desk, and it's just right.
The one unflavored green tea with the absolute richest flavor of all is Dilmah's Ceylon green tea. It's a little darker than Golden Tips, but has a much stronger grass-like taste. It's delicious. It easily stands alone without flavor.
My current favorite flavored tea is Dilmah's Moroccan Mint green tea. A freshly brewed cup of that has a delicate mint taste and is easy to drink without sweetening. It takes a little longer to brew to get the mint strong, so it's a balancing act between stronger mint with bitter green tea or lighter green tea with weaker mint.
Until a few weeks ago, my previous favorite flavored green tea was Twinings Green Tea and Orange. It's still nice, but since the massive, persistent headache started a few weeks it's been giving me bad acid reflux for some reason. It's orange flavor is easily overpowered by the tea if it brews too long. The worst is sometimes the orange bits get oily and the sides of bag stick together, then tear while making it, so the bits of tea leak out and really stay in the hot water way too long...
The Twinings Apple flavor is good, but the apple is even more subtle than the orange and must be brewed very short or it's lost altogether.
One other I drink periodically, is Dilmah's Cinnamon flavored green tea. It's good, too, but is best loaded with honey. That's why I've cut back, I'm trying to reduce the sweets and sugar, and this tea simply needs honey to really enhance it. Then it's like a a baked good with lots of cinnamon, not like a cinnamon hot candy.
The last green tea worth mentioning is Ten-Ren, a green tea sold by Costco in the U.S. My mother used to recommend that one and once a friend brought a box of 100 of them for me here in India, but 99 of them were gone years ago. I found one late last year in a box of other teas, that must've been left over from my days at First Insight when I packed my personal things at the end of my career there. Ten-Ren is fantastic tasting, but too difficult to get here... And it survives longer brewing times, since back then I didn't know about doing it quickly.
The main problem with the short brewing times is the feeling that after spending the money to get teabags, I only use them for 30 seconds. It feels like I'm not getting my money's worth, despite being fully aware that the end result is best short.
In this way, it's not unlike fancy lingerie, expensive for very little material...
Both are effective by being brief, and both lead to a delicious *sluurrrrp*!