In Avengers: Age of Ultron, Tony Stark "loses" his AI assistant, Jarvis. Since time was of the essence, he loaded up something that looked like a backup/older assistant, Friday.
However, in Civil War, we can see she is still being used, and Jarvis was not recreated by Tony Stark. Does that mean she's as good of an assistant as Jarvis was (or better), or is there another reason Jarvis was not recreated?
Out-of-universe answers are welcome as well.
In Captain America: Civil War, during Tony's fight with Captain America at the Winter Soldier base in Siberia, Friday informs Tony that he cannot possibly beat Cap in hand-to-hand combat. Tony then asks Friday to analyze Cap's fighting style and provide him with countermeasures. In barely a minute or two, Friday has provided him with the information, and Tony quickly turns the tide of the fight. It's unclear if she's actually controlling his suit, or merely instructing him, but her information is vital to Tony's ability to stay in the fight.
Jarvis has shown the ability to locate weaknesses in enemy weapons systems, such as when he instructs Tony to target damaged components in Obadiah Stane's Iron Monger suit. He's also shown the ability to control Tony's Iron Man suits independently, and eliminate multiple targets with their weapons, as when he assisted Tony in fighting Aldrich Killian's Extremis brigade. However, I don't believe we've ever seen Jarvis do something as complex and urgent as Friday's countering of Cap's fighting style. From this, I conclude that Friday's capabilities - at least in terms of assisting Tony in operating his suits - are equal to or greater than Jarvis's. In areas other than combat, there may be other supporting (or contradictory) examples, but I found this an easy comparison that seems to line up directly.
It seems likely to me that Tony is always improving his AI assistants. Even if Friday was a lesser prototype or side project to begin with, after using Friday for a few months, Tony could possibly bring her up to the level of capability that Jarvis previously had. From her performance in Civil War, I think we see that this is the case.
F.R.I.D.A.Y is one of the many back-up A.I.'s that Tony Stark has created.
Tony created a variety of different AIs, most likely that he has used at different periods in his life or perhaps something else to differentiate them.
We see for instance when Jarvis is thought to be destroyed in Age of Ultron, that there are a number of different "back up" AIs for Tony to choose from:
In the above screenshot you can even see a memory stick labelled Jocasta (upper left).
Assumedly Jarvis was an AI that learned over time to be able to better serve Tony. This means that many hours would've went into "training" Jarvis to learn Tony's various idiosyncrasies among other behaviors.
There is also the fact that Tony really treats Jarvis like the butler he no doubt grew up with, not like an AI. Now that the Jarvis AI is housed in a body, perhaps Tony feels that he really is his own person now.
Since Tony is still using F.R.I.D.A.Y as far as we know, it's reasonable to assume that there's no glaring issues with the A.I. I couldn't imagine Tony Stark doing well using something sub-par after all!
