i machine semi profesionally.
i use all types of cutters depending on the job
high speed steel is great when cutting softwoods as you can get a sharper edge to the blade. cutting speed/chip load being correct or the blade will dull very quickly.absolutely useless on mdf , laminates and some hardwoods, they are so abrasive the cutter will be blunt in no time.
carbide tipped. great for general work on softwoods, hardwoods, mdf etc. the cheapies are ok and are considered disposable, however if you get some cheap diamond card files (about £2 off ebay) you can redress the edge a few times. (ive had more trouble with shanks snapping than blades blunting)
Solid carbide. the same sort of finish but seem a lot more durable. i have 3 roughing spirals i use daily which give a very nice finish and will cut through anything!
pcd. (diamond) cost a fortune to buy but will outlast anything as long as you dont drop them etc! ive had one 45degree chamfer cutter on my big router for 3 years cutting edges every day on laminates, hardwoods.
the worst thing for any cutter is running it at the wrong feed speed (too slow) this causes a heat build up and can kill any of them quickly. a lot of my tooling requires feed speeds of 5 to 8 metres per minute!
this is an example of correct cutting speed with a 12mm spiral in oak.
http://www.youtube.com/watch?v=8O391...eature=related
obviously a lot of hobby machines wont run this fast and require smaller tooling. (this is my hobby machine just been converted to mach 3 ) when you find your not breaking tools any more and you want some extremely sharp top quality cutters have a look at itc tooling. search google
they are not cheap (approx £20 for a 2mm cutter but the quality is superb)