Your question is about gloves, but it's a question which leads to some more important considerations. I stand to be corrected, but the content that follows assumes you're relatively new to boxing, or at least to sparring.
If your goal is to prevent brain trauma (and I argue here that this should be your primary goal), the most important factor for you to consider is the way in which you spar.
As the previous answers and comments demonstrate, there are a range of views and practices when it comes to glove and headgear selection, and equipment choice is important, but it pales in significance when compared to the question of whether or not you should be sparring in a way that recklessly or intentionally exposes you to regular head trauma.
When you're a beginner, and once you've overcome your fear enough to step into a ring a 'fight', you quickly learn that getting hit in the head isn't actually all that painful; that you can shake off relatively hard hits.
You might be different, but it's been my experience that most boxers are prone to bouts of reckless machismo, especially when they're sparring to an audience in the gym. Playing 'Raging Bull' and fighting on; 'taking the hits like a man (or woman)', is actually not that hard, but it can make you feel like you're tough, a lot tougher than your body actually is. These facts conspire to make sparring a very dangerous activity; especially when considered over the long term. Immediate injury is also quite possible, especially if you're like me and get dehydrated relatively quickly. Dehydration reduces the amount of fluid surrounding your brain and renders it more susceptible to impact-related harms.
Whether the gloves you are using are light or heavy, whether you are wearing headgear or not, if your sparring practice is regular and allows or encourages repeated impacts to the head, you are at risk of causing and sustaining serious cumulative damage.
You may feel as though learning to take a punch is vital; and that's the sad truth about boxing: you do need to learn to take a punch if your goal is to become a fighter. But no matter how strong your neck muscles get, and no matter how used to head impacts you get, you can't train your brain to take a punch.
Much of the pleasure of boxing - indeed one of the responsibilities of a boxer - in my humble opinion, is in aspiring to hit without getting hit. This principle can be extended to your sparring partners too; for if you care about their wellbeing, you should also aspire to learn how to be able to hit them but, without needing to actually hit them.
If you want to be a competitive boxer, you will need to spar hard; to attack your opponent's head and to defend sincere attempts to knock you to the mat. Ask yourself if this is something your really want to be involved with.
But, seeing as your question refers to 'friendly sparring', it is entirely possible to gain immense pleasure and release from boxing, and to become very skilled without regularly causing or sustaining damage; to learn movement, defence, offence, strategy and to have a whole lot of fun, by learning to spar safely.
With a bit of practice (and some fundamental 'no-go zones', such as the kidneys), body sparring can be very, very intense yet quite safe. Techniques can be learned and the body can be conditioned in ways that enable your limbs and torso to take a lot of impact safely. Once you have the ability to control your range and to create openings to the head without capitalising fully on them, body sparring can extend to incorporate head shots that are 'pulled'. You will generally know when you have your opponent 'cold'; there is no need to actually make any but very light contact. There is something very satisfying about knowing you could have knocked out an opponent - and knowing that they know you could have knocked them out - but in restraining yourself from executing.
Unintentional hits will occur. Freakish clashes will happen. Injuries will be sustained. Egos and aggression will occasionally erupt. Learn to master your emotions and your techniques. Make sure that when you spar with someone new that they share the same notions of safe sparring as you do. If they start hammering away at you without control, leave the ring and find someone else.
