Which operating systen is best android, windows, ios, blackberry or symbian?

ios is amazing but I honestly think the nexus 7 and nexus 10 are some of the best tablets out there. It really depends on what you want it for tho

ANDROID IS THE KING OF OS s!!
people simply don't know about android because they have not experienced it. once you become a hardcore android user you will turn into a fandroid!!

the best tablet are
asus transformer infinity
nexus 7, nexus 10
galaxy note 10.1
sony tablet s
asus padfone 2

gsmarena is the site for a viewing correct specifications.

See my friend both ios and android good
and there are many tablets that you can buy under this budget
1)ipad 2
2)nexus 7
3)asus transformer series

Ios!
because only ios is unsed in most branded mobiles at present!