Trying to find the ins and outs and seeing which I like more.
Guilty Gear is better but let me explain why.
Characters: Guilty Gears cast consists of unique characters that were well designed and some made of music references. Every character had some sort of depth to their character and served some purpose to the story and were all around well-designed. I could go further but I'm not gonna make an essay out of this. Blazblue's characters... while well handled, are anime stereotypes when you get right down to it. That's not to say they're bad, as to say they're not incredibly unique and diverse. Sure, some of the characters are well handled and even genuinely unique while the others are blatant stereotypes that have no depth or serve any real purpose to the story or are just basically Dan made into a ninja. The Villains of Guilty Gear have always had an air of mystery around them and were also well made and somewhat terrifying. These were villains that you knew nothing about and they didn't try to spout shit about how fucking awesome they were. Blazblue's villain... as much as I like Terumi... I can't take him seriously. He's there to be more funny than he is to be threatening, it's only when he's really Hazama that he actually has some mystery and that's because Hazama is more or less his Jekyll to Terumi's Hyde.
Gameplay: Here's where it matters, both games have a fun combat engine that consist of pulling off crazy combo's and over the top fun. But again, it goes to Guilty Gear. Why? Guilty Gear doesn't rely on gameplay gimmicks. Guilty Gear's gameplay gives you a set list of techniques to use and never will you see one that involves doing unfair shit to the opponent. Blazblue is the opposite of this, IT EVEN GIVES YOU A BUTTON FOR THIS. While the drives do add some fun and depth to the gameplay, the problem with things like the Drives are they are not only too easily gamebreaking but just completely and totally stupid in how they fluctuate. I'll use a good example, take Ragna's Drive which lets you sap health from the opponents, this is not a bad idea. Whenever you hit someone with the drive they will lose a fairly small amount of health and Ragna will gain it back. Jin's however is an example of easy gamebreaking, his freezes people. While this is not a bad idea on paper, it lasts too long for the opponent to use yet another drive to freeze the opponent for longer and leave them in a perpetual state of inaction that will put them in too low of a state to make the fight even remotely fair. And don't get me started on Arakune and Nu, good lord.
Music: It's the same fucking guy doing badass music for both games.
So before anyone says I'm being biased, I am actually looking at the game from a reasonable point of view and describing the problems.