Being daft I have a 25 year old Dremel, a cheap Dremel clone, and a Proxxon IBS/E.
The Dremel has worked fairly well for it's life, reliable and very useful, within it's limitations, which are few. One limitation which induced me to buy the Proxxon was the Dremels spindle play when using it as a toolpost grinder. The Dremel was usable but only just. The Proxxon has a better spindle arrangement, which reduces this effect. It doesn't eliminate it. I think that a "proper" toolpost grinder may be required to get good toolpost grinding.
The Proxxon is definitely quieter and smoother than the Dremel.
The Proxxon has better quality collets (hardened steel) compared to the Dremel (brass or Al. Alloy). There are about 5 or 6 Proxxon collets, covering the same range as the 3 or 4 Dremel ones. From memory the range is from about 1.0mm up to 3.5mm.
I'm thinking that it's down to what you want, the Proxxon is definitely better than the Dremel, but not by a huge margin, but it's about 1/2 the price of the Proxxon. The freely available "clone" Dremel is /was about 1/2 the cost of the Dremel, and is noticeably lower quality in pretty much every area, although it's still useful.
So it's pretty much a case of "you pay the money and you take your choice"!!
Best of luck
cheers
Bill