You will with out doubt get many opinions on this subject. The main differences in the two brands you've mentioned are that most S.P. regs are piston type where most Aqua Lung lines are balanced or (over balanced) regs. These differences may seem insignificant at first glance, but you really need to do more research. There are many, many websites dedicated to this very subject and my advise would be that you start checking out the resources available to you through the web. Both types of regulators have their strengths and weaknesses and depending on what type of diving you plan to do in the future this information will indicate the better choice for you.
Don't rely on opinions from a page like this only. Do your homework and you won't be disappointed, but then that will be true of all your decisions as you go forward or downward as the case may be in your pursuit of scuba diving.