I'm in the lucky position of fitness being part of my job, and if I'm going to go to the gym for a 50 minute session at lunch, a) it's 10 minutes walk from my office and b) my boss is there too, and he's younger and skinnier, so I get to kick his ass occasionally.
We do a variety of different circuits - today's was Metafit which is quite warming, but it can be Bodypump, functional fitness, step aerobics, outdoors, or a traditional 15 stance multi discipline thing with grid sprints to finish. All of these (I reckon) have combined to get my MSFT score up to 10.7, which is a 2.5 improvement on where I was last May (VO2 Max from 40 to 50 in 10 months).
It doesn't matter what gym class you go to though. There are loafers who are there to be seen at all of them. I can't keep my hands in place to do burpees because of the lake of sweat around me, but the bloke beside me is barely breathing hard. Yes it's annoying, but I'm doing the work, I'm making efective use of my time, so I get the smug points when I kick his ass on the grid sprints. Again.