How to know when to pick a gun

So, in game i have seen people (including myself) ask what weapon they should use for the next round. Today i am here to help you determine what gun to pick.
1. Know what the map is like, for example: Warsong_ctf is up next, i know it is a big map so a sniper would best suit the map i am about to play on. Also say i am playing erosion i won't use a sniper considering how small of a map it is.
2. Gamemode: A big factor in determining what gun i use is gamemode. I say this because normally during
infect I don't use a automatic unless it's minigun. A big difference for me in a map is if it's tdm or ctf. On hijacked ctf considering it has a longer time i will normally use minigun. But considering there is less time in tdm i would use crossbow if it was tdm.
3. Gun preference: If you want to use a certain gun for any gamemode go right ahead. Sometimes i let loose and use a iso on erosion.
Now here is a list of guns 41+ should use for tdm
Tdm/Ctf Big map: Iso, dissasembler, skullcrusher, msr, dragonuv.
Tdm/Ctf small map: Model1887, minigun, skullcrusher, dissasembler, ak47, lementation, flamethrower +all smgs.
Oic: executioner, python, deagle. If you have all donater tacticals and what not use molotovs and c4.
Infect Big map: raygun, minigun, model1887, typhoid, spas24, lementation, ump45, pp90, p90.
Afterword: I hope you enjoyed my guide on picking the right gun for whenever. Yes this post is a little pointless but it is to help people, it is my only intention.