Yea, it's a big cloud of subjectivity this one, but an interesting question I think.

You definitely see less of the traditional TBBS in current-gen RPGs, but the demand is still there. I'd say that the action elements were introduced in the genre to try and make it more mainstream, but don't quote me on that. Regardless, if you want my opinion on a good battle system suitable for a GS title,I'd recommend a blend between that of a game such as Lost Odyssey (A fairly traditional TBBS with a few innovating and modern elements) or perhaps one that feels a little less static such as it's seen in Arc the lad: Twilight of the spirits (ps2). In my opinion, both are more than decent, and both present a system with enough depth to keep a player excited for many hours. Something like that should be reasonable for a hobby project too.

Yes, it's probably a good thing to keep development difficulty in mind for such a battle system, and my personal guess would be that a real-time action-based battle system is harder to develop than something that is built around turns. Turn-based, you'll avoid all manners of tough topics, such as path finding, complex animations (running + swinging a sword + jumping?) and complex camera handling.

All in all, the more static you make your battle system, the easier it gets to control, and the faster it is to develop. As for what's cooler, that's such a scary opinion-based matter, I'll keep to my opinion alone: yay for Lost Odyssey and hurray for Arc the dude.

That's just my opinion though