Personally I use them all and can never detect the difference but others say they vary a lot. The flat Hermesetas pack fits in the pocket so I find it useful when out and about
I use 1 Sweetex for tea. For coffee I use a quarter spoon of sugar and can almost count the grains. I dont know why I chose Sweetex, probably it was the cheapest but its perfectly ok. I use Sainsburys SlendaSweet in plain yoghurt. I dont buy those small fruit yoghurt pots such as Muller, Ski etc. Full of sugar and a lot lot cheaper to create your own.
I've started using Stevia, which is made from a natural leaf and should not have all of the toxic stuff that other sweetners have. But watch out, any sweetner in powder form is 95% maltodextrin and only 5% of the actual sweetner. This is the case for splenda, sweetex, stevia, the lot. So I use the tabs crushed up or have recently bought liquid stevia which is great and very sweet!!