I'll agree that this is rare to happen but, if you have a team all trying to spam rush (all push the exact same path) Natascha can actually be useful, if you have another Heavy backing you up and at least one medic to try keep you both running long enough to have some help from your side (this would apply to clan matchs mainly and any clan that tries to all push the same point with a heavy on the map is asking for a bit too much). But otherwise yes Natascha is less viable thanks to it's lowered damage (if the slow "damage" stayed a while longer it would be more viable, for the simple reason of making easier targets)
Sandman should only be used if you want to piss someone off or you know you can make the stunning hit for someone to capitalize on (yes it can happen)
Backburner works well if you can play a sneaky game and actually get behind them
CAD should not, I repeat, SHOULD NOT be used in any CP style match as it may actually incure you a ban (especially if you ninja cap)
Ubergun is a tad pointless (although if you go battle medic I suggest Medigun, Blutsauger and (can't be assed to remember the name so...) "other saw" as this will, if you can play the style, give you both light health regen per landed shot, the ability to still tank up the heavies and can also lead to the hated "Near-Perm-Uber-Medic-Duo" (other saw gives 25% charge per kill)
(as said before) Only use the Ambassador or Huntsman if you are proficient at headshots at closer range
BONK! is fairly pointless really so try and avoid it
FoN is a decent weapon if you know how to use it properly (if running with the Sand' you should use this anyway as you loose double jump thanks to that silly bat) but you shouldn't use it for going past double jumps as there is nowhere you need to triple jump too
Flaregun may be called a cheap weapon, but if you can land it reliably use it
Only use Jarate in For Fun matches as it can be hard to make sure the crits get used properly by the team
Razorback should only be used if you camp sniper
Use the boxing gloves if you so wish
The Dead Ringer (if you can get it through random drop) is great for when your still learning spy as it can help you get a second chance on your mistakes
Axetingusher is a tad pointless but if used in conjunction with a flaming opponent can be fairly useful for some ncie finishing crit damage
Sandvich should also really be avoided as you will barely ever use it (only useful if your team has no medics or you plan on solo heavying)
Also as a tip: If you see a chance to use any of these tactics and your not setup for them, a quick run into the loadout menu (there is a hot key for this by the way) can help you change up before you next spawn (if you do this while at alive at spawn it will not change till next spawn)
{Soldier and demo missing because of lack of trial with new weapons (and poor engie as he has no update

)}
Edit: Igonre that link that was there I typed all that in notepad and had a link from earlier on in my night in there I forgot about