I owned a Newton 100, 120, and use a 2000 right now. I also have an old Palm.
The only reason not to buy a Newton is it's size, it is like a VHS cassette. So if you need something that is really small and that you can put in your pocket, you have to get some kind of Palm device.
But that is really the only reason. The Newton can do much more than the Palm and handwriting recognition is much better. There are several email clients, web browsers, TV remote controls, spreadsheets, wordprocessors ect. You can even sync it with iTunes now (it low quality and it does not have a 5 gig HD, though). You can use a modem card, ethernet and several different memory cards with the Newton. And just to make it clear the only difference between the 2000 and the 2100 is the memory (both have backlights). An upgraded Newton 2000 is the same as the original 2100 except the different logos on the case.
So if you want to carry a little extra weight, get a Newton! You will not regred it.