What kind of campaign should be set to get maximum reach? CPC or CPM?

Depends on Campaign Objective:

If Purely Branding (and with descent budget): Then CPM, as all the Supply partners accept CPM bid price. 

If Branding + Performance OR purely Performance: Then CPC, as post impression render metrics of clicks, bounce rate, session etc can be captured giving better insight on reach on campaign objective.

well depended on the budget provided , so CPM will be great to reach in top point matched with your target

if you want to sell products, them CPM and if you want your audience to come on your site then CPC.

but in my opinion CPM is better way to reach more audience because poeple mostly recognize images so CPM is the way you can show your ad with image and they will come to your site. Remember your product should be attractive.

CPM buy is the best to increase reach. However if you want quality users, CPC campaigns work best.

Are you building brand awareness? Then "CPM"

Are you looking to drive conversions - read an article, subscribe to news, download a pdf/software, sell a product or services etc , then "CPC"

Therefore it depends on your goals and objectives