A US Air Force colonel wrote in 1995 that
It is true that insurgencies that resort to terrorism continue to vex security forces. But the weapon of choice for the terrorist is not the kind of armament the Second Amendment seeks to protect; rather, it is the bomb.
As you can probably guess, that analysis has as its main topic something else, so the issue of terrorist choice of weaponry isn't developed much further in there.
There's another (2010) opinion in the Economist along the same lines, but which also goes into putative reasons for it:
This brings me to something I've always wondered: why are terrorists so attached to bombs, as opposed to other engines of death and catastrophe? Assassins sent to take out specific targets use a wide variety of interesting tools, particularly poison. But terrorists seem to be strikingly uninterested in poison. They want to blow things up. One could imagine a few reasons for this. Explosions are good for getting media attention: they leave lots of good visuals for the cameramen afterwards, which is important since you can't invite the cameramen in advance (so they usually miss the moment of the attack). And there's a metaphorical satisfaction to a bomb. It's a blow delivered. Suicide bombs are even more effective because they present no immediate target for retributive justice, which can create political pressure for the victim country to engage in excessive or futile punitive military actions; this is often the very goal of the attack. With gunman attacks, the response and the hunting-down of the gunmen is itself a satisfying act of retribution, and that satisfaction can blunt the target nation's willingness to get involved in the drawn-out cat-and-mouse game the terrorist wants to lead them into.
Of course, it may be difficult to, ahem, survey terrorists in a systematic fashion, but is this view that terrorists prefer bombs as their weapon of choice (assuming they get to chose, they might be restricted in some circumstances) largely uncontroversial?