A few days ago someone asked in Mumble when is the best time to take the Block talent. You’ll notice I deftly skip answering that question to discuss a broader topic: General talent selection.
For quick matches with pick-up-groups, talent selection isn’t all that important, in my opinion. It is likely best to build for maximum damage no matter what role you have selected. There’s no guarantee of what other team members you will get (I think once I actually did get 2 support 2 specialist 1 warrior/assassin).
However, when playing with other Strats members, you can select your heroes according to what talents compliment each other.
For example, some warriors (Johanna, Tyreal, Chen and Stitches) can choose the Amplified Healing talent for an additional 30% healing received. It might be a good idea to choose this if you are grouped with someone playing Li Li who can put out lots of healing. Li Li also has a talent where her Cloud Serpent attacks will heal the hero it is assisting (I assume Amplified Healing works for this as well; not fully tested).
If anyone knows of other heroes and talents that synergize together, please add them here.