Kind of hard to say what is "best" because all paint is different.
Meguiars D151 for maximum correction
Optimum Poli-Seal for light correction and a carnauba look
Werkstatt Prime and Zaino AIO for paint in near perfect condition and as a base for sealants.
Both D151 and OPS can be used on paint in excellent condition as well, so they'd be more versitile if you require a wider range of correction than Prime or ZAIO offer.
I agree Poli-Seal is an awesome product. I just washed my truck yesterday and the beading was still tight after 3 mo. but it's only for light correction.
My only real AIO experience is with Optimum Poli-seal but I never looked further and I am on my 3rd bottle. Just a weekend warrior that does a few details for money on the side. It's the ease of use and the high gloss that has me sold. As others have said, it only has minor correction abilities but it's such a pleasure to work with and offers a great gloss at the end.
I suppose DG105 is like an AIO and I've used that plenty but it has no abrasive to it. just a great sealant with good cleaner property.
DG 105 is kinda like Z5. Z5 supposedly has swirl removal capabilities in it, but I've never seen it work like that. Just like I've never seen 105 do anything other than be a awesome sealant.
If BigJim were here (where's that slacker been lately, anyway???), he'd throw some Hi-Temp AIO in the ring. Hi-Temp has a couple different AIO's that are supposed to be pretty good.
+1 for 151 for correction. I like ZAIO for everything else.
Terminator Paint Sealant is supposedly able to remove swirl marks. I can say, I have used it after 105/orange on the PC and it was able to remove micro-marring and leave an awesome surface finish. This product is super underrated. Strangely my favorite application of this product is boats, works great.
I use KAIO, it works as the product is intended. It will leave a clean slick surface that you can add anything too.
It will remove light oxidation and embedded grime from the paint, trim and chrome. What ever Klasse won't do I usually have a "specific use product" to do that.
I've used D151 on two of my black daily drivers w/ success. An orange pad will remove moderate swirling and fine scratches, while a white pad will remove light swirls and finishes LSP ready. I can't comment on the durability as I top it on the next wash.
As a bonus you get a big ol' jug (1 gal) for a nice price; a plus when using the KB method as you don't worry so much about use of product during priming.
I use KAIO it's the only AIO I've used so for me it's great. However seeing the responses here, it seems like OPS is a great product, and it's cheap!! Might give it a try.
I use Poli-Seal. Works great for me, but I don't feel it has very good corrective ability when applying by hand. One day I will buy a machine and see if it can correct my soft honda paint.