Hi,
A bit late to this thread.
I make chips for a living by day and fool around at home when I get the chance with benchtop 8x14 lathe and a Grizzly G0704 mill. So I get to see and use stuff at both ends of the endmill spectrum. US made tools are pretty good, but are far from the only game in town anymore. Others make cutters as good or arguably better and cheaper these days. At work I can justify the best because time is money and shaved seconds can literally count. At home, I have more time than money. And tooling costs come from saved potato money like everyone else.
First carbide vs HSS. Can't live without the stuff at work, particularly in the smaller sizes of 1/2"-12mm or less. And carbide endmills will run just fine on a benchtop mill at those speeds and feeds we can from our machines. But I don't find it cost effective at home. Too much money for the amount of use it will get. So I prefer HSS endmills at home because they are cheaper and will give nearly as good of performance for the money spent.
The basic Cheap, Cheerful Chinese M2 HSS endmill can run from junk to pretty darned good. When buying them look at the dealer's reputation more than the Made in China mark. A good tool seller will tend to buy from factories that make better stuff. A step up from Chinese M2 is the Chinese M2Al that is becoming quite popular these days. I've been buying them a fair bit for home use. While I will tell you M2Al isn't the equivalent of M42, it is a very noticeable step up from the run of the mill import M2. And at a minor increase of only a couple dollars per cutter, has become my go to choice at home.
If you troll places like eBay for cutting tools, sometimes you can find good deals even yet today. When I start trolling, I look for odd sizes. Few want 9/32" endmills it seems. But they cut just as well as the more costly 1/4" and 5/16" you find on the "Bay. Look closely at the imported cutters. Not all come from China. Korean endmills often sell for little money but are every bit as good, (or better), as US made tools. Polish and former Yugoslav tooling is good stuff. So are Israeli brands. All often sold at discount because they aren't well known to hobbyists. I also look for resharps. Why? For some reason, even "professionals" want new. But to me, resharps are like gold. I recently picked up 3 resharp solid carbide endmills, (two 3/8" and a 3/4"), for less than the cost of one new 3/8" carbide.
2flute vs 4flute endmills. Each have uses that the other isn't as good at. I use 2 flutes when I need chip clearance. Like milling softer, stickier materials like aluminum or plastics or in confined spaces like slots or blind holes. The downside to 2 flute cutters is slower feeds and depths of cut due to flexing. And poorer surface finishes when side milling with them. The 4 flutes can be fed faster because of two more cutting edges and will give a better finish when side milling. But often do poorly in soft, sticky plastics and non-ferrous metals. So a decent selection of both types is a good thing.
Dalee