The sweeteners I like to use Intense Sweetener or Protaste, Rod Hutchinson and Kevin Nash sell both products. I don't know if there is any difference between Rod's or Kevin's sweeteners, but I like them both just as much. I suggest if you are in a shop that sells both, you buy the cheapest.
Intense Sweetener is a saccharine based product and therefore tends to give a more intense sweetness to your baits than Protaste.
Because of this, if I am using spice flavours such as Mega Spice, I always use Intense Sweetener, as I like more sweetness in my boilies with the spice. If I am using cream or fruit flavours I will use Intense Sweetener or Protaste. If I am using fish flavours with a fishmeal base mix, then I like to use Protaste. This is because it’s not quite so sweet and will let some of the fishy taste come through. If I am using a fishmeal base mix with fruit or cream flavours etc., then I will use either sweetener.
With Intense Sweetener I like to use it at levels between 1.0 to 4.0 mls per 4 to 5 eggs, depending on the depth of sweetness required. Protaste I like to use at 1.0 ml with fish meals and between 2.0 to 3.0 ml with other flavours and base mixes.
If you are on a tight budget, just buy Intense Sweetener it’s cheaper that Protaste. Use it at 1 ml with fish flavours and between 2.0 to 4.0 mls with the rest.
Please note, that besides the two companies listed above, other bait companies produce excellent sweeteners. Mainline, Solar and Nutrabaits are just three that spring to mind.