They were both elite drivers, but manu's size and ability to draw fouls made him better- there's a reason so many teams were able to shut Tony down by packing the paint / using a longer defender on him. Still have to admire Tony's exceptional speed and skill finishing in the paint despite his size disadvantage. Manu was elite at drawing fouls, something the team is sorely lacking now.
Manu obviously has better range, and Tony eventually became a very good passer too.
Re: playing with/against 2nd units, it has pros and cons but manu used to close against starters regularly and he was pretty damn good at it. When manu started his stats went up and I'm pretty sure when Tony came off the bench his stats went down, can't be bothered to look up the numbers now.
For me, offensively the difference is that Tony was more dependent on matchups, while manu was more dependent on health due to his reckless style. assuming both are healthy playing vs a strong playoff team, I'll take manu.