can anyone tell me what the best window cleaner is to use on mirrors for cleaning in a bar with heavy smokers.

I think I would use a vinegar and water solution on that!

Depending upon just how much nicotine build up there is you can do as Heavenlyhomes recommended or you can wash the mirrors with a little dawn dish washing soap in warm water, squeegie then apply the vinegar solution as needed to obtain desired results

We like wintergreen alcohol.

http://72.10.47.74/uk2005/detail.php?ID=21799

I use easy glide. Works well but is mainly meant for a squeegee. It's available at home depot for about $7 and should do the job nicely. I would use a simple 10 in strip washer http://72.10.47.74/uk2005/detail.php?ID=22007

It has a non abrasive side which will allow you to break up most of the gunk build up.
Steps I would do as follows.
1) wet mirror with soft side of strip washer
2) flip strip washer over and use scrubbing pad really well.
3) squeegee mirror
4) repeat process 1 time for quality assurance.

Should take no longer then 5 minutes and your done. The quality soap will help in future cleanings.

I like vinegar, water, a dash (tsp or so) of eco-friendly dish detergent and a few drops of wintergreen essential oil (or any other scent you like)
The dish detergent cuts through the muck well, but if you add too much it gets streaky so be careful.