I've tried a few out, decidedly underwhelmed with P21s & the Megs stuff. Poorboys Super Slick & Suds is pretty impressive but I found it left my paint looking a bit washed out. I'm currently using Pinnacle which lathers up nicely & leaves my paint looking very rich & glossy.
I always use Auto Magic's Wash & Wax. It's costs me $12 for a gallon and suds' up really nice. Smells like bubble gum. http://www.automagic.biz/soaps.htm
I on the other hand find that using the right shampoo makes a *huge* difference, especially with regard to wash-induced marring and the shampoo's effect on my LSP.
Griot's Car Wash for me, with Meg's #62 and #00 as my second and third choices.
I agree with Accumulator...the Quality does matter....to me the lubricity is what counts...I want a shampoo that feels like oil on the paint....also one that is gentle to LSP....to me NXT is harsh
I use Groit's and Duragloss ..both have superb qualities..slick...gentle but good cleaner...rinses very clean...
Meguiars gold class for me. I find that eagle one wash soap leaves a better shine, but the gold class just makes the car look rich. Also tried rainx soap, mothers', poorboy's SSS, NXT and turtle wax platinum, but the gold class just takes the cake for me.