I use Google, but from a marketing perspective I still get some traffic from Bing so I try not to ignore it.
Bing's search results are so similar to Google nowadays that I don't bother with it...when they ran the ad of comparing the 2 search engines, I started using Bing, but eventually, wiki and youtube results were all over the place and there was not much difference.
I prefer google because it has faster than others. I use Gmail, G+, and Google webmaster tool for my website, etc. but nowadays, Bing is growing faster in social media and we can't forget that too..!!
You don't know how bad is Bing unless you use it for a good amount of time. I decided to give it a try for a day and it drove me nuts with the absurd results it gave!
I tend not to like new things, no particular reason beside I go with hat I know.. maybe I'd like it, but the advertisements seem more obnoxious the way they show up on bing
I use google because I am used to it, but bing is way more convenient (at least for me) for searching and browsing images, because if you want to change your searh keywords, you don't have to go to the top - the search field is always at the hand. I also like that when you type bing.com you can put a space and write what you're looking for - it saves time (yeah, I know that you can make it your default search engine and you won't even have to type the adress, but in other cases...) And I like that you can watch video just running a pointer over it - saves time if you are trying to find specific video and have to go through many of them.
Google, because google would recommend search results relevant that seemed good by google through a process google algorithms and google of penguin.