I never know what it means when people write they are "trying to learn" FMQ. If you are truly a newbie -- meaning you have less than 8 hours of practice time at FMQ -- I would go with the Blue water soluble marker. The purple marker will start to disappear before you get very far, causing lots of frustration. Chalk or Crayola Ultra Clean crayons will rub off, causing missing parts of the line, which will make it more difficult to follow.
If you don't ever wash your quilts and have already done some practice pieces, then I would recommend either white chalk (the cheaper the better) or Crayola Ultra Clean crayons (I use the white the most often because it will come out with a damp cloth, but doesn't rub off as readily as chalk does). Be sure to buy a sharpener for either one.
The other 2 options depending on your eyesight are a Hera marker (you just score lines in the fabric -- it's similar to a bone folder; there is nothing that transfers onto the fabric) or Golden Threads papers that you punch the pattern into using an unthreaded needle & then pin to your fabric & use like a dot-to-dot that tears away once you've finished the quilting.
If you do wash your quilts, I must say that I've had the best luck with Crayola Ultra Clean markers -- but they do need to be washed to get the marks out.
The one thing I really do not recommend at all is the Frixion pens. I've known too many people -- both on QB & in real life who have had marks reappear in transit to quilting competitions, if the weather got bitterly cold, if they didn't try to iron away the marks for more than a year, or sometimes for reasons unknown. I personally had an experience with them when I received a marked quilt kit. I didn't realize it was marked with Frixion pen, rather than pencil, as was traditionally done. So I ironed it & the design almost entirely disappeared. But I remembered that cold could bring the marks back. 5 minutes in the freezer & the marks were as bold as ever. Fortunately, it's just a practice piece, but I know I can never take that quilt outside for football season or keep it in storage or my car where it can get very cold. I can't submit it to competition as it wouldn't survive the cold temperatures of the atmosphere high up where planes fly. There are just so many limitations; it just really doesn't seem very practical to me.
There are documented instances where the blue pen also resurfaced. It works by "disappearing" into the batting -- which, of course, means that in certain circumstances it can (& has!) reappear either on the back or the top of the quilt. It doesn't happen very often. It's a far safer choice than Frixion pens. Many competition quilters use blue pens & very, very rarely have them reappear in transit. Since you don't want to wash the quilt, that would be what I'd recommend.