The SE/30 is the favourite in terms of speed and performance, however if you're going to be using the machine for simple productivity tasks like word processing then pretty much any compact will do the trick. The Macintosh Classic is a very good machine for this as it has the 1.4MB floppy drive, (thus can use PC floppies), and Classics are much more readily available on the market cheaply.

I use my Classic for word processing and spreadsheets and I find I get much more work done on it than any newer machines simply because it is simple with fewer distractions. System 6 is a very clean operating system and a basic install will normally boot in about 10 seconds on my Classic. They are solid little machines and seem to soldier on no matter what.