He is strong enough to be one of Konoha's best shinobi but weak enough to be beaten by Pain.
He was not weaker than Pain. Pain/Nagato himself said that if it weren't for him having the element of surprise thanks to Jiraiya not knowing that he had the Rinnegan, than Jiraiya would've defeated him. If Jiraiya had managed to escape rather than stay and die while leaving a message, then fought him again later on, chances are that Jiraiya would be able to beat him now that he has an understanding and knows his secrets.
You can’t really say for sure… In terms of comparison Jiraiya is definitely weaker than Nagato, since he couldn't beat Hanzo and Nagato beating Hanzo single-handedly, granted Jiraiya was just getting stronger, and in contra, even weaker than Naruto whom beat Nagato/Pein even without the knowledge and having to figure out the systems during the fight, though the problem is Jiraiya did not face all six paths together. Conclusively, you can’t really say. So he is definitely one of the strongest ninjas ever, just unlucky (*note: This is a personal theory that started with a personal claim of twins. Feel free to consider this rubbish)
I can say that for sure because it was specifically said by Nagato himself in the anime and the manga. Chances are, Nagato also beat Hanzo because of taking him by surprise with the Rinnegan's other abilities. And there is also the fact that the battle between Jiraiya, Tsunade, and Orochimaru against Hanzo took place when they were still young, so Jiraiya now, as opposed to back then, would be much more experienced and had time to develop his various abilities and he'd also have his Sage Mode to work with.