Following please find my analysis:
If you already have Tor on board ( Unix / Linux ), you could easily extract following information :
# cat /var/lib/tor/cached-descriptors | grep -i ^finger | sort -u | wc
7184 79024 445408
7184 uniq descriptors for me.
# cat /var/lib/tor/cached-descriptors | grep ^platform | sort -u | wc
138 800 5376
138 different platform, it is what you are asking.
# cat /var/lib/tor/cached-descriptors | grep ^platform | sort | uniq -c | sort -h -t 1
...
121 platform Tor 0.2.4.22 on FreeBSD
131 platform Tor 0.2.4.19 on Windows 7
145 platform Tor 0.2.4.23 on Windows 8
159 platform Tor 0.2.4.21 on FreeBSD
167 platform Tor 0.2.4.22 on Windows 7 [server]
170 platform Tor 0.2.4.21 on Windows 8
180 platform Tor 0.2.4.22 on Windows XP
196 platform Tor 0.2.3.25 on Windows 8
259 platform Tor 0.2.4.20 on Windows 7
395 platform Tor 0.2.5.5-alpha on Linux
396 platform Tor 0.2.4.23 on Windows 7
409 platform Tor 0.2.5.6-alpha on Linux
427 platform Tor 0.2.4.21 on Windows 7
537 platform Tor 0.2.4.22 on Windows 8
864 platform Tor 0.2.3.25 on Windows 7
1094 platform Tor 0.2.4.21 on Linux
1146 platform Tor 0.2.4.20 on Linux
1465 platform Tor 0.2.4.22 on Windows 7
2143 platform Tor 0.2.3.25 on Linux
4857 platform Tor 0.2.4.23 on Linux
6443 platform Tor 0.2.4.22 on Linux
Here you can see 6443 platform Tor 0.2.4.22 on Linux
<-- most popular configuration today. More than 80% - is Linux.
Probably, there is some level of error in this computation, because grepping is not done by unique fingerprint. You may browse this information on your own.
On one hand, being a sheep in the herd probably not a great idea. The best option is to use the OS that you know better.
On the other hand, if you encounter any problem you could resolve it much faster with most popular configuration.