Which polish/wax for yellow?

You have one of those colors that no matter what you do it's really not going to show your hard work to well. The only thing I would suggest switch to a carnuba to give you more of the wet look. Strip off Ziano and since you all ready purchase on line check out http://www.specialtymotoring.com/clearkote.htm and pick up some Clearkote Vanilla Moose hand Glaze and Clearkote Moose wax. This will give you more of the wet look but it won't as long as a synthitic(sp?) wax like Ziano. It's a trade off you have to live with.
 
Well, it depends on the look you wish to achieve. For a really shiny, reflective appearance, you will want to stick with the synthetics such as Zaino or Klasse All-in-One teamed up with Klasse Sealant Glaze.

If you desire a warmer look, go for a carnuba product. Two of my favorites are Poorboy's Nattys Paste Wax and S-100. The S-100 is available from most Harley-Davidson shops.

If you are going for the ultimate in appearance start reading up on Autopia. It will benefit you a great deal, it will be a little intimidating at first though.