Well there are as many opinions about different kits decals as there are different kits.
Of all the different kit brands I have built, the only ones I will say are totally un-usable are ICM. Every kit I have done of theirs, the decals have been falling apart as soon as they hit the water. Many decal problems arise from age and how the kit has been stored. If the kit has been stored to warm or in sunlight, the decals tend to dry out.
Tamiya tend to be a safe bet, safer than most, at least.
There are various decal solutions you can use to make decaling a more pleasing experience, but not fool proof.
If you want to get some extra decals, as a back up, you might like to consider some sheets of generic markings. Serial codes, ID letters, and national markings. If you build a bit of every thing, this can be a hard way to go as you will need a good few. If however, you build say only British aircraft, the amount of sheets needed comes down to a manageable amount.
Also, you have found a pretty good forum here with loads of helpful members. So if you do find you have a decal that goes to pieces on you, you can ask on here if there is any one that has a spare. Post a request in the bits bin section.
Let me take this opportunity, to welcome you to the forum.
Ian M