This is the best Guilty Gear title in the series, hands down. If you're new to the franchise, this is the perfect game to start from. If you're a longtime fan, this should be a no-brainer.
Nights of Azure is for Gust fans, plain and simple. It's not a bad title by any means, but there are issues that can mar the overall experience. If you're on the fence, wait for a price drop.
Rabi-Ribi is a fantastic love letter to Touhoumania fans, but at its core, it's an exceptional platformer that's so well designed it'd make Daisuke "Pixel" Amaya blush. Rabi-Ribi manages to blend multiple concepts together and distil them into something entirely unique, which is a rare sight these days. The difficulty is firm but fair, and the optional help solidifies that. Its Touhou-inspired cast may be too much for some players, but if you can stomach through its aesthetic, you'll experience one of the best indie titles of 2016, bar none. You'd be doing yourself a massive disservice by not giving Rabi-Ribi a shot.