I think we need to be careful to remember exactly what Steve wants to use the keyboard for. A songwriting tool first and foremost.

A built in harmonizer is not needed for this (and, IMO, are little more than a gimmick for OMB's). Anyone recording a song is going to use real BV's...

There are some important questions that need to be asked before the right choice can be arrived at....

How well do you play, Steve? (Is the quality and size of the keyboard important at all?)

What style of music do you write in? (WS's are better for modern, cutting edge styles, arrangers are better at 'meat and potatoes' styles)

Do you intend to lay guitars down as real instruments, or do you need an arranger with realistic guitar parts? (Yamaha S900 is a good choice if you do)

Do you intend to record FINAL parts, or just make demos? (WS's, though much more complicated, ARE what they use on CD's much more than arrangers)

Do you have ANY experience making recordings with a computer sequencer and a WS? (If not, an arranger will get you up and running MUCH faster and easier than a WS)

Come back with these answers, and we can perhaps advise you better...