This is going to be an opinion piece: I would choose TACTICS.
A prime example would be Afghanistan, where a bunch of natives armed in many cases with 100 year old rifles and improvised explosives, is causing damage to the American military, a much more technically advanced force. Technology can give you advantages, but if the tactics are flawed in the use of the technology, it doesn't matter.
I have to agree 100%...........tactics and above all TRAINING...over reliance on failable technology is actually causing a substantial reduction in "skills" in many armed forces.
Over reliance on GPS systems has had a huge effect on the ability of combat troops, company level Officers included, in simple basic skills such as compass and map orientering, which one would consider an invaluable skill for infantry and armour branches. The ability of combat troops to effectively shoot WITHOUT having the miriad of sight systems on the weapons has been greatly reduced, and as any electronic powered or enhanced optics can and will fail...again presents a substantial detriment.....
Could a typical "Somali" pirate as you used in your question even be capable of using the "latest" technology with any effect...highly doubtful...simply due to an entire lack of understanding and familiarity with the technology....
Could the SAS or for that matter any other trained military force effectively use WW2 weapons to great effect...absolutely.....it strikes me as funny that you would use an example of WW2 weaponry as being ineffective...perhaps some familiarity with the variety and capabilities of those weapons would be of benifit here...the Brit/Ausie/Canadian/S.African/Indian etc Lee Enfields may be older...but they are highly accurate and can with familiarity and training put substantial number of aimed and effective rnds. down range ( example "the Mad Minute" that was part of Commonwealth training). The American M1 Garand was and is still a devistating battle rifle, the German Mauser K98 was very acqurate and effective...and certainly the BREN, MG42, STG, MP40 and a huge variety of others could still in the hands of a trained soldier be more than a force to be reconned with...
In short, it comes down to the inherent ability and training found in modern military troops, with their ability to integrate technology that will always stand head and shoulders above mearly having the technology in the hands of untrained and non capable fighters.
I guess the old adage of "anyone can use a weapon, what makes a warrior is the ability to use their mind as well"
Cheers,