An awful lot of the decision is decided by... exactly what style do you write in?

Current, cutting edge styles are better served by WS, IMO. But if you write in a more classic, or simple songwriter style, an arranger is the better tool.

At the price point you think you can manage, probably a Yamaha S900 might be your best bet.

Another take might be; if you are just concerned with WRITING the songs, the arranger is by far the best tool. If you want to RECORD the piece (for final release, not just a demo), a WS might be the better choice.

But if you are a complete newbie to sequencing and recording, the learning curve on an arranger is a fraction of what a WS is going to make you have to deal with...

Me, when I'm writing, I want as little technology in the way as possible. That's the NEXT step of the process! In fact, 90% of the time, I just write at a piano....