User blog comment:RoznosicielCiast/Exhaust vs. Ignite at top lane/@comment-24.85.89.41-20130222120917

Depends on the champions you're facing/playing

Personally I like if at least 1-2 people has exhust on the team, usually one for bot lane and the other in the hands of solo top

At least one person should have ignite on a given team though as you said mid's the best, plus if the adc takes exhaust they become that much better at dueling and the support can take heal or vice versa.