sugar substitutes - to use or not to use

For years now, I have been using the so called "zero calorie" sugar substitues in my tea - equal, sugar-free etc. Since I drink numerous cups of tea a day, adding sugar to all of them is simply not an option - and i coud never get used to tea without sugar

I read and hear lots and lots of differing views on how healthy (or not) is the use of these. While obviously it is better to not use them at all, i want to know exactly what risks i am running by using these, how much is safe to consume daily, which ingredients in them should i look to avoid when i choose my brand etc.

Any views or info on this that anyone would like to share?