Depends on the situation, type of player you are, or weather this is a joke class it's being run on, and the overall setup you're going for with the setup for the sniper of choice.
HBS isn't really necessary to me on a sniper, PERIOD. Claymores are enough of a notice usually if you're a camping sniper, to let you know you're about to have a close encounter, in which case, your secondary will be coming out to hopefully handle it.
It's better off on a class which WANTS to get into the mix where enemies may be located, like a run and gun setup. Snipers are better off playing the range-game.
Sure, you may encounter someone who may know somewhat where you are after being killed by you, or after you've let off a shot on their radar, but they may be running Ninja the next time if they're smart, and watched the kill-cam. Which I hope you were also smart enough to re-locate your position, to not get caught like that to begin with.
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As for Thermal, thermal in my eyes is best suited specifically for maps like Wasteland, or Underpass. It is also handy to utilize in a "counter-sniper" setup if you run into a problem with an enemy sniper using it, but with SP. Slap a WA2OOO on with SOH+CB+W/e you desire, then add the Thermal, and you've a good opportunity to nail them, before they nail you. EASY head-shots, and you have all the time you need to line the shot up (being you have CB on this) with this type of setup.
If your situations do not readily call for use of thermal, you're best off playing with the basic "power sniper" setups using SOH+SP and then FMJ for the attachment. A stealth sniper class though, will run different, but if you run the right sniper that is.
So basically what I'm telling you is, it's okay to have a thermal sniper for counter-sniping, and for proper map abuse (forget the idiots that call it cheap, it's called playing tactically when done if necessary) then have at least another setup for sniping normally. HBS is useless to you as a sniper.