which type vaccum cleaner is used for cleaning window grills?
It isn't necessarily the type of vacuum you need, it's the attachment(s) that it either comes with or are available for it. The attachment type most applicable for the scenario(s) you are asking about is generally called a "dust brush", of which there are multitudes of types and sizes.

 

As for the brand and model of vacuum unit, there are way too many choices to list; a product-review web site may be able to narrow your search to the most reliable.

I prefer the "shop vacuum" canister type unit, as my experience has been that they are the most powerful versus cost (but they are less versatile, they are not for vacuuming carpets).