It depends on where you are, but 9/10 times I find Wifi to be the superior choice over 3G. Both in terms of speed AND battery life.
For me 3G tends to be around 2 or 3 Mbps and my wifi at home gets me more like 20 or 25. Even "slow" public wifi tends to be around 4 or 5.
What do you mean by latency?
A) Imagine a car that can go from 0 - 60 instantly but that's as fast as it can go.
B) Now imagine a car that can go 90, but it takes 5 minutes to get going that fast.
Car A has low latency but also low speed.
Car B has high latency but also a higher speed.
Which would you rather have? Well, if I'm going 3 miles away car A is the clear winner. But if I'm driving 3,000 miles across the country I'd rather have car B.
So to put it in iPhone terms, having "car" A is great for e-mail and web sites and other small files. But "car" B is better for downloading large photos or streaming videos.
But of course, having choice 'C' (a car with low latency AND high speeds) is best. But I'm explaining it by showing you an 'either-or' case. Often in the real world you DON'T have to pick and can, in fact, get the best of both without having to pick.
