Android vs Ubuntu
Android and Ubuntu represent two of the most popular forms of Linux. For a lot of people, they represent the hope of mainstream success for free/open-source software.
 Target Market
Android is an operating system made for mobile phones, which then expanded to target tablets and desktop and laptop computers as well .
Ubuntu is an operating system made for desktop and laptop computers, which then expanded to target tablets as well.
Each is used mostly on the devices for which it was originally designed and has limited popularity elsewhere.
Android is available in unmodified form and also available on particular phones with proprietary user interfaces developed by the phone maker.
Ubuntu is available in unmodified form and also available with different user interfaces developed by free software communities (for example, kde, xfce, and lxde).
 Popularity in the Linux world
Android is a newer operating system serving a newer segment of the market; it seems to have gained more wide acceptance than Ubuntu.
Distrowatch lists Linux distributions for desktop/laptop/netbook computers. Of these, Mint(based on Ubuntu) is the most popular and Ubuntu is the second most popular; many of the other top distributions are based on Ubuntu (and Debian, the fourth most popular distribution, is the base on which Ubuntu is built). Ubuntu is much more popular than Fedora, the third most popular distribution.
 Competition with Apple
Android competes with iOS for success in the smart phone market. Android phones are more popular than iPhones in terms of how quickly people are buying them, and in terms of how many are in use. (Until recently, iPhone was still in the lead in terms of total number of devices in use).
Ubuntu has just begun to compete in the tablet market (against iOS operating system and the iPad device) and has competed with apple for many years in the desktop and laptop market. according to http://en.wikipedia.org/wiki/Usage_share_of_operating_systems Ubuntu AND other non-android linux distributions represent about 1% of the market (among operating systems that are used while viewing the web) while OSX represents 7% of the market.
 Tablet Devices
By far the most popular tablet devices are Apple's iPad devices. Neither Ubuntu nor Android has proven to be a substantial competitor at present.<a matter of personal opinion