i believe irfanview is by far the best.
this is what you can do to see various exif info, overlayed:
IF you only want to see a few EXIF values while you browse however, I would suggest you display them on the Status bar at the bottom of the screen. Open Options >Properties/Settings and select the Viewing tab. At the bottom of the dialog box you will see where you can type in "placeholders" for displaying various items of data on the status bar. Click on the Help button beside it to see which placeholders you need to use. You can also add text to identify what they are if you like.
I think what you will probably want is ...... ISO $E34855 F $E33437 Exposure $E33434
(the default iso tag didn't work for me, i tried $E2 for Nikon's ISO tag, and it worked; canon, others etc. will be different probably.)
for full screen:
Take a close look at the options for showing text in fullscreen mode (Options, Fullscreen/slideshow). You can select specific Exif fields to display, which will let you focus on just a few items of interest while browsing in fullscreen mode
here i used $E2 again and i can see the iso.