I've used Models I, 2, III, 4, and 4P as well as the Model 100 and the WP2/3.
I would have to say that I still like the 4P best for it's flexibility and implementation. Mine is packed up in storage now, but I had replaced the disk drives with double-sided ones, added an external HD, and the XLR8er Hitachi processor upgrade with banked RAM. For a Z80 system, that had a lot of power, and especially so with Roy Soltoff's LS-DOS operating system though it also could run CP/M and the Model III OSes. The Model 100 is a close second, and for word processing I do like the WP/2 (especially with a NADS box for convenient storage extension on both of them.)
