I've used both numerous times
I like both
The 5 x 5 routine is good, I like the way the goal is to push more and more weight (much more measurable and satisfying than loosely trying to add 1 or 2 kg to your bodyweight over a training cycle as with HST). I really surpassed my strength expectations using this routine - I managed a bench press of 115kg x 5 at a bodyweight of less than 90kg (6'3 tall - so not a big frame) and was really chuffed.
In the end, after 3 consecutive training cycles I had to give it up - I don't think I ws made to squat heavy 3 times a week (that many sets at least) - got nagging pulls in my hips etc. when doing mundane daily activities (and I was using sensible form).
With HST I was pleased with the weight I put on. I put on 4kg (approx) over 2 consecutive cycles (16 weeks = 2 rest weeks). Was happy with that.
Really enjoyed training this way. The first week / week and a half I thought 'is this really going to work?' lifting light weights... I think you just have to put your faith in a routine and follow it through then assess at the end.
The start of my journal shows (in my sig) where and when I put the weight on using HST in those two cycles.
Just trimmed some fat off and am now using HST again (the third time).
Don't get too caught up in trying to find the ultimate training program. Pick one that seems sensible, train consistently, eat well, rest... when you get to the end of the training cycle/routine (and you gave it a fair chance), see if you enjoyed it, and got the results you were after. If you did, do it again (if it ain't broke etc...), if you want to try something different give something else a try... you should be able progress with most of the tried and tested routines in the stickies on this forum (IMO)