Instead of the added complexity of implementing multiple hash algorithms, if you're using something like bcrypt or PBKDF2 you can just increase the work-factor which makes the attacker (or indeed your application) do more work to calculate the hash.
There's a risk, depending on your usecase and traffic levels that if you crank work factors too high, you can impact the users perception of your performance (e.g. a login operation might appear slow)
Which is actually better in terms of time required to brute force(as in which takes longer) ? Two different fast algorithms with moderate work factors or one algorithm with a pretty high work factor ?
well AFAIK you can keep cranking the work factor as high as you like, so realistically one algorithm with a high work factor is likely to be better as it's a simpler thing to implement and has no drawbacks in terms of security.
There's a risk, depending on your usecase and traffic levels that if you crank work factors too high, you can impact the users perception of your performance (e.g. a login operation might appear slow)