Szczesny was never bad. A few dodgy spells maybe. If he's a bit more mature he's probably worth a punt considering he's free. Every signing is a punt after all.
I have a feeling if he'd never played for Arsenal and we'd been linked to a Polish international who's played for a good Spanish club in the top 4 for a few years then spent 2 years at Roma then Arsenal fans would probably be bang up for signing him with Cech being questioned now.
I've really never seen anything from Ospina to make me think he's any better than Szcz ever was and he's a lot shorter.
Ospina should really be looking to leave and be a #1 somewhere else after 3 years here in and out (mostly out). It would probably be a good time for Szcz to return and really fight for his place with a realistic chance of taking it back and if he fails then he can move on.