What tile adhesive to use on plasterboard walls

I am looking for advise on what tile adhesive to use on our bathroom walls, and floors, The whole house is plasterboards upstairs and wood sheet floors, ie plywood, not the best finish in the world but some tile shops said that We need to use flexible adhesive and others said not to.

Keeping in mind tiles bought on budget so ensuite tiles €150 and bathroom €250. The normal tile adhesive, already mixed is between €15 to €20 and flexible, not mixed is €30 to €35

We are going to use flexible on the floors, but do any tilers out there think we would get away with normal stuff on walls.

I know the grout, etc could crack if the walls move excessively, but what are chances of this actually happening. and whats the worst that could happen if it did?

My experience personally and in the job (working for a large contractor) is that flexible adhesive is used on backgrounds which are likely to shrink, flex or move- plywood will do all this. Plasterboard is dimensionally stable, the only movement that will occur in your stud walls will be as a result of shrinkage in the timber studs. This shouldn't be a problem. The only areas where this can be an issue is in corners where cracks can develop and open up. It is good practice torun a bead of silicone up these vertical joints in corners anyway, especially in shower enclosures. To sum up use flexible adhesive on floors and regular adhesive on the walls.

thanks carpenter, however, i bought flexible adhesive for floors and walls today at half five, so will go with that, it was much more expensive, got 20% discount so only paid 25 for it for 10kg bag, will be a bit smarter though when doing the ensuite.