For grammar and spelling, dedicated service Cysill wins!
http://www.cysgliad.com/cysill/arlein/
If you want to get the “gist” of a piece of text, Google Translate can be handy.
http://google.com/translate
I should come clean and say there is no battle being fought between Google Translate and Cysill. It’s just about using the right tool for the right job.
In particular, if you’ve been tempted to use Google Translate to check your spelling or grammar then Cysill is much more suited to the task. I have it in my web browser’s bookmarks toolbar, ready to be clicked when I’m writing email… or my latest literary masterpiece.