Which device is going to be best option for online ad campaigns in future(Smartphone or Laptop), why?

I am agree with the below answers and the other thing is that, Smartphone will be going to be a best option for online ad campaigns in future comparing to Laptop. This is because, Smartphones users are increasing day to day and we could find the more active users in Smartphone than the laptop. Since, we have the option for the targeting the device, I would say that Smartphone will be the best option for targeting the campaigns in the Digital Marketing.

this is as different as "book in hand and book on computer screen" Moreover, we need to see where the smartphone ultimately will lead to... (a gaming product or secure business product) if it can offer a business security in future than it will create irritation if a businessman receives irrelevant ads on smart phone...   

Well this is quite complicated and tricky to answer. Well as we know that no other thing can generate the business like facebook do. I would suggest to go for both options. All you have to do is1 Ad-Campaign (Sponsored) for website like Facebook where you can reach to masses and for the Phone app. This is because not to forget Phone batteries dies as early as in5 hours, secondly on phone the awareness will be restricted to the population. Also, facebook on phone generally works slow as compare to laptop. If you have both the options it will help reaching to maximum clients. 

I will prefer laptop though. 

I think it is smartphone device because it is very easy to handle and operate.  You only need load and full battery charged.  while the laptop device is bulky and besides you cannot use it when there is no electricity.