Oscar Garcia is interesting. Surely more/better experienced than Unzue, but much less than Valverde, Sampaoli, or whoever else has been linked to us. He says all the right things (and seems to believe them too) and would try to embody Cruyff and Pep as much as possible. However, there's simply not a reliable sample of his work to actually ascertain what kind of manager he'd be for Barcelona.
He was great with Juvenil A when he was here. From what I read, he was great with Maccabi Tel Aviv too but that means almost nothing. Red Bull Salzburg is his most indicative body of work but it's always hard to analyze with a club like that. Winning the league doesn't mean much at all, OG hasn't had difficulty with it. Qualifying for the CL is much harder, probably above the club's capabilities. They've been knocked out in playoffs both seasons that he's been there. I (tried) reading some translated Red Bull Salzburg forums and it seemed like Garcia needed a good amount of time to experiment and adapt his tactics/system to get the most out of his team. They said that the team performed well defensively but were somewhat lacking in attack, though he improved over time.
It's extremely difficult to make a 1:1 comparison between his Salzburg side and what his Barca side would be. Red Bull are far above any of their league rivals but the technical level of most of his players is probably low. That'd probably affect what kind of tactics he could've implemented there. I'd imagine that OG would try to play Barca-football wherever he coached, it simply may not be feasible at Salzburg. It'd obviously be much easier at Barcelona where most of the players know the system and are well fitted to play that kind of football, though we can't be sure that Oscar Garcia has a deep understanding of those tactics as they pertain to top level football against diverse and competitive opponents across competitions. Pep looked a much better coach at Barca than at any of the other clubs he's been with, perhaps this environment can rightly equip Cruyff-inspired coaches to play the football that they envision. It's easy to play dominant Barca football like Pep did against the likes of Granada at the Camp Nou. It becomes much different against CL caliber opponents who have different systems and approaches but are very effective with them.
Overall, I think Oscar Garcia is the right type of coach with the right mentality. The question is whether he's a GOOD enough coach, and that's a fairly big one. He'll try all the right things, we just don't know if his intelligence and understanding of the game is great enough for him to succeed. His arrival would probably be key for younger players trying to get chances. Aleña would certainly get ample attention from OG and others like Marlon, etc. would get chances after Mathieu is gone.
IMO, Berizzo would be a safer but still strong choice to consider. His Celta have performed well over the last few years and play pretty good football. He's also shown tactical flexibility as players like Nolito, Krohn-Deli, Charles, and Santi Mina have all left over the years. He also gives chances to youth players, though I think Oscar Garcia would surely be more committed in this regard. I prefer the mentality/style of Oscar Garcia to Valverde, though the latter is much more experienced and safe. Berizzo is also more suited to what Barcelona needs, though both he and Valverde have had similar positive impacts on their clubs. All 3 are clearly superior choices to Unzue as far as I'm concerned though.