The best caulk I have used in the past for wet areas of the bathroom is 100% silicone with a mildew inhibitor. (i know... How can it be 100% silicone if it has anything else in it? )
[EDIT !!! - I found some advice here and if you use the silicone, the following applies, but there seems to be a better alternative ESPECIALLY for long term maintenance and touch-ups. Howard Emerson linked to this caulk :
The method of applying it is a bit different, from one user i read here:
Still, it looks good and I am going to get some myself. I have had good experience with silicone , and can't afford too much extra time for application - but that's only because i install an acrylic system almost every day, and with acrylic and a caulk primer, the silicone is great.]
At Lowe's you can usually find GE Silicone II.
Whatever brand you find, make sure you get the kind that also says "Kitchen and Bath" or one that says the cured silicone is mildew resistant.
While this kind of caulk is not a water-cleanup type, it WILL stay flexible for many years (forever?)
I have seen it in clear, white & almond, but i am not sure about other colors.
A 1/8 hole at the tip is usually large enough, and if you are pumping out a thick bead to fill gaps, you may want to use a tool to remove excess caulk.
I like to cut a ring from the end of the tube (at first you won't be able to - until you have used a bit from the tube). You can then squeeze that ring to the size of the finished bead you want and scoop along to remove the excess or globs that sometimes develop as you slow down and re-pump the caulk gun. Once you have a fairly consistant bead, you can use a finger to further smooth it, but first spit on you finger and use a light touch. When you feel the caul starting to build up under your finger, or dragging a lot, pull off and wipe with a paper towel. wipe well to remove any caulk (the caulk will clean your fingertip nicely and wipes off fine. Rewet your finger and continue.) This sort of smoothing will not compromise the seal, but will give it a gloss and remove any edge that might collect soap scum , minerals etc. Depending on how the qwalls go together, you may actually be able to just scoop all the surface caulk off between the panels if they overlap.
Have plenty of paper towels on hand and if you get caulk outside the area you want, wipe it off immediately.
If you need to touch up a seam, either do it quickly (adding a tiny amount o the surface of the bead and ten smoothing in) or wait until the caulk is fully set (to avoid rippling the surface of caulk that has begiun to 'skin-over"
Cleanup is difficult with 100% silicone on a cleaned surface, and you want to be sure that whatever you use to remove it will not harm the surface.
The only thing I have used is denatured alcohol (removal from acrylic), but i am not sure if that is ok for your wall material. Usually I am stripping out seams, and use a flexible snap-off blade to carefully carve the rubber seam out.
If you worry about gouging the surface, or you are working away from he corners and rubbing with isopropyl alcohol and denatured alcohol are taking too much time or work (it is not easy or fast), you can look at a couple i have found but not tried myself :
I would try these on an out-of sight spot if possible to make sure no bad reaction will happen during the soak-in time.
The bad thing about silicone is the fact that it is hard to remove once cured.
The good thing about silicone is ... the same thing
Well, i have to copy this and rewrite it as a guide now LOL--