Unless you do lots of synth programming, for my money, arrangers have always been a better choice than a "workstation" in any studio that does simple recording, or songwriting. Having the patterns, and drums styles are a great creative motivator, and most quality boards have all the sounds you'd need for an average project. For more specific things, there are soft synths. In the programming category, I think Korg has the most to offer. It's a deep architecture for synth creation, and sound manipulation. Yamaha has great samples, but less tweak-ability. (in the arrangers)

To go even simpler - With all the sounds, and loops I have in Logic, I can record almost any project with a simple midi controller (Akai MPK-249) and my trusty iMac.