Why do particle physicists use the $h\rightarrow{\gamma\gamma}$ decay mode rather than $h\rightarrow{b\bar{b}}$? Just wondering, the $h\rightarrow{\gamma\gamma}$ decay mode is often quoted as being most sensitive to measuring the mass of the Higgs particle, why isn't the $h\rightarrow{b\bar{b}}$ decay channel used given it's significantly larger branching ratio?
 A: I'd say that this claim is specific for the current experiments at the LHC. We collide protons there, and the protons are made of quarks and gluons -- strongly interacting stuff. You can even say that there are already $b$-quarks in the proton.
So, when the protons collide, this strongly interacting stuff produce events that are similar to the genuine $h\to b\bar{b}$ events. So you need to find a way to distinguish between your Higgs candidates (called signal events) and those strongly-interacting-protons events (called QCD background events).  
Now, keep in mind, that we are dealing with 0.8 billion collisions per second. Most of those collisions are from QCD background processes. There is no way we can record and reconstruct all of them. For that reason we have triggers -- fast electronic circuits that do nanosecond-fast rough reconstruction and decision of whether to keep an event.  
On top of that, you have a problem that you never really see a single quark or gluon flying from the interaction point. Those strongly interacting particles hadronize forming jets -- streams of particle shrapnel flying roughly in the same direction. So, you need to reconstruct each of those particles, try to associate them into isolated jets and hope to infer at least some properties of the original hadron. That really reduces both your your energy and momentum resolution and your signal/background separation. 
When it comes to $b$-quarks, we are a little lucky: hadrons with the $b$-quark have a lifetime significant enough to fly away from the collision point and create a secondary vertex that you can notice (if we are lucky enough) and conclude that the jet is probably $b$-orginated. Such techniques are called the b-tagging and some of the b-tagging algorithms are even implemented at the trigger level. 
But even with all this, it is still nearly impossible to see the Higgs in the $b\bar{b}$ channel -- check that recent CMS paper (Phys. Rev. D 92, 032008). Authors had to resort to VBF production mode to have some extra particles to rely on, notice how important the trigger is in the development and how they still barely see it...   
A: In order to get a good mass accuracy using the gamma gamma channel one needs to measure well the gamma energy in the electromagnetic calorimeter which can easily contain all the energy. The four vectors have measurement errors but not missing energy.  b  and b_bar decay weakly to  a number of particles including neutrinos and the subsequent decays end on  the stable up quarks, with several more neutrinos in the process. Neutrinos are only detected with fits and therefore the errors in defining the four vectors of the b and b_bar will be much larger than the ones for the gamma gamma decay channel.
