Bing is installed by default when there is IE 8 or other fresh install of windows system or browser. Ask is 3rd party service and hence we have to search for it on our own. Ask is meta search engine and there are some cool results from it as well. Bing is just rebranded live search. I use more of google so i can't compare ask or bing. But if you've to choose then go with bing as it is one search engine with some good features.