Solved

When to use Medium Tyres

Is there any situation in which medium tyres are the best option?

No, but I still use them anyway :) Australia, Bahrain, Europe, Singapore & Dhabi

They're not the best in any situation but can be part of a winning strat in a select few tracks if executed well. I've seen 2 managers in top leagues win while using Mediums in one stint in Spain and Abu Dhabi respectively.