I use the Mirka Goldflex. Supergrit.com

I use a Mirka Molded Palm Sanding Block &
Mirka Abranet 5" H&L Mesh Discs
80-1000 grit.
Lasts for ever, does not clog and can be rinsed out and reused

Wayne - full disclosure, I sell sandpaper. So, there isn't one correct answer. I sell a lot of Mirka to some very high-end woodworkers. They seem to like the Abranet for the reasons stated above. I other customers that prefer 3M gold discs in a 320 grit for scuff / between coat sanding. You can save a little money (sometimes) with the very inexpensive no-name import stuff like the 1st guy's recommendation, but when you start to have finishing problems, you won't know if it is the prep (sanding), spraying, or a bad batch or poor mix of your spray material. Staying with a quality abrasive eliminates one step from the occasional problem-solving process. Now if you just do cheap work, cheap stuff is OK. If you want to turn out a consistent high-quality product, stay with high-quality, consistent supplies.
If you want to call me & mention WoodWeb, I'll give you an extra discount. Ask for Steve Sr.

Well Steve. I've been finishing for 20 years and bouncing around within a lot of sandpapers. I've tried lots. Expensive, cheap, middle of the row. This is what I've settled on after years of finishing. Never had a problem that I could attribute to the sandpaper. It's inexpensive and lasts pretty well. Cuts nice. But all I'm talking about is the 320 and strictly for finish work. I use a wood block with some self stick felt on it as a cushion. Works very well.

I wouldn't have recommended it if I ever had problems or if it didn't work well. I wouldn't buy it either.

3M, the Grey stuff works well for my applications. Not sure if the Eagle Brand is still available but it worked very well too.

3M Purple

That really depends, I use festool brilliant 2, sialac silicon carbide with 103 hole discs, Wurth Zebra, Wurth Arizona and Wurth ICE! But my favorite cheap sanding discs are the Indasa Witheline they are so cheap and so good :)

Buy the stuff made in europe. They have a different grading system. Something like 95% of the grit on a disc is the 320 grit. Whereas even the US stuff(with the exception of the expensive 3M pro stuff) is something like 60% correct grit size.

I've been using the Mirka Gold sheets, 6" discs, their Abarnet disc and depending on the project their maroon scotchbrite pads.

All of their products are good value compared to all the other brands besides Klingspor. Our plywood supplier also happens to carry Mirka, but I also buy it from other sources.

Definitely get stereated gold(better) or white

norton or 3m. whichever is most convenient to purchase. the off brands ave a much shorter cutting life. i dont have a solid mirka supplier in my area but it is nice sand paper

I've been using Norton for a long time. I used Mirka as that is what I was exposed to starting out. Good stuff but more expensive. What Adam said about the grit sizing is right. Their 320 is probably equal to 400 of other mfgs. I think in the past especially WB finishes were much more sensitive to contamination from grit adhesive. Supposedly the Norton adhesive was/is not friendly but I've never had a problem.

Bart,

The euro grit size vs US/everybody else makes a huge difference with clogging,abrasion speed and consistent depth of scratch.

Its visible under finishes.
High quality 320 grit is not visible. The cheaper paper you can get coarser grits mixed in with the graded grits. Meaning there can be 180/240 grains on 320 paper.

I agree that some of the WB manufacturers have changed their formula's to work with the white stereated papers. Back in the 2000's we had to use the gold or there could be fisheyes depending on the brand.

I still use all gold products, because they work, and Mirka only makes gold.

If you read the boxes of 3M and Norton often the prograde stuff is made in Europe.

I love the Abranet paper but have trouble buying it. Who has the best mail order pricing on it?

Surf Prep has never been called "inexpensive no-name import stuff" before. We have gone more than 10 times longer than the net abrasive in quiet a few applications. contact me if you want more info.

The problem with specialty abrasives is availability. Where are you going to find a surfprep/mirka supplier who is open on a saturday at noon when you accidentally run out of sandpaper. Even on a weekday you would have to wait at least one day after you place the order to receive the product. After a quality brand name, longevity has more to do with the backup pads that you are using.

We work through distribution and we have great coverage throughout the nation. Many of them have that kind of relationship with their customers.

My local Wurth Wood Group Stocks the SurfPrep, all pads and accesories. I have never had a problem getting it.

A&M supply is 2 hrs away and the rep will get it to me the next day if I need it. I always keep ahead several boxes anyway.

As Adam said, it last a lot longer then the other major brands you mentioned. I have tried them all. No build up. Just hit the piece and/or the pad with it a little air and its gone.

If you are having trouble finding a good source, we stock the Mirka Abranet as well as the Mirka Gold in Hook and PSA, as well as the 3M Purple, cubitron II, and 216U and 236U Gold discs. We can also get Norton and provide excellent pricing on all if you call Steve 215-699-2224 and mention WoodWeb. Regarding the European versus American grits, the difference is how the grit is measured. the number, say 320, is the number of holes in a 1" square screen (mesh). In Europe, it's the number of holes in a square centimeter. Since the centimeter is slightly shorter, it will be finer. The US, or CAMI 400 grit is very similar to the European, or FEPA P320. (Whenever you see the "P" in the number, that indicates FEPA grading.)

Steve,

I agree with you on the grit spec. 220 grit = 240 grit.

The bigger issue is the one I describe above. If you look at typical Norton paper at a hardware store, you can visually see different grit sizes on the same paper.

Not an issue with the prograde papers, but it can be with cheap USA or cheap paper in general.