I am admitted towel-aholic. I have hundreds, and I just have one car so its definitely a subject I have experience with. My recommendation would be to focus on several categories of uses for towels, and then buy towels to dedicate to each category rather than to focus on the towels themselves first. You can break down the categories into dozens of uses and get into serious overkill, but here is what I would start with and some recommendations in each. The other reason to have categories is so that you can wash them only with towels of the same category. This is important because you don't want residue from a wax or sealant removal towels to contaminate drying towels. As Mike Phillips said in a post way back, get enough of each category to make a washer load; you don't want to wash 4 towels at a time and you don't want to mix types in the washer.
I'm going to focus on towels from AG/ACC with one exception.
Interiors - easiest and most economical is to buy a 36 pack of the Costco yellows. You don't need fancy towels for interiors if you are looking for a basic intro setup.
Drying - use drying towels only for drying, and wash them by themselves so they don't get contaminated in the washer with spray wax/QD or anything else than can reduce their absorbency over time. I'm a big fan of the Griots PFM and the Gyeon silk, but many people like good quality waffle weave towels like the guzzlers or other brands.
General Paint towels, such as spray wax/QD and general paint use. The yellow cobra junior are probably the best towels for this are are a good value. I would never be without these towels.
Gold Plush Jr. Microfiber Towel, gold detail cloth, buffing towel, microfiber buffing towel, micro fiber
Paint - polish/wax/sealant removal. Towels such as the grey 530's or pink 600's are great for this. Also the AG edgeless towels are really good and are inexpensive; they come in multiple colors so you can keep wax and sealant separate from polish if you like.
Forrest Green Edgeless Polishing Cloth
Wheels/Tires - definitely have dedicated towels for this, and only use them for wheels and towels. Black general purpose towels work well for this.
Microfiber Wheel Detailing Towel, wheel buffing towel, all wheel towel, utility towel, shop towel. Or, here's a budget trick that works - dedicate 6-8 or so Costco towels for this and the first time you wash them put a really dark MF towel in with the load of costco's. This will discolor the gold costco's with dye, but wont hurt the effectiveness of the towels, and then you can tell them apart.
Sacrificial towels - engines, etc that you will throw away after one use. Costo's.
If you waterless or rinseless wash, you will need a dozen good quality plush towels. I prefer something in the 600 gsm range. This setup will be the most expensive, but if you shop around you can get good value.
Hope that helps.
