To be honest, I never loved too much the BU set, that could be crippled beyond repair with careful switching around and maybe a status absorber; however, with BW2 Technician came and that was a huge blessing for our favourite mushroom. Okay, the SD set is uninventive and used everywhere, but still remains the most effective IMHO. CSC is right when he says that you need to gamble a bit; however, other Breloom sets like SubPunch (which I like too, but that's another story) have much more surefire checks / counters since they lack the raw power Technician gives (for example Gliscor, that can take Seed Bombs all day and cannot be slept, but is murdered from +2 Bullet Seed), and may even be a liability other than an asset for the team (imagine Gengar switching in on Substitute, then Substituting itself, and start trolling you with Disable...). Also, Choiced sets are now much more viable with Technician thanks to the awesome side effects of Low Sweep and Force Palm, that can incapacitate the switch in and keep pounding on him. Of course, Poison Heal Breloom is still viable, but it's not as good as it used to be in my opinion; it still have a niche as a surprise set, or a physical attacker that can safely absorb Scald, but I find myself using it very rarely, and never with awesome results.
Not accepting rating requests anymore. Sorry!