Until recently I had just assumed that heavy weapons were the way to go in Edge of the Empire. Both skills use Agility, so assuming you have equal access to both Ranged Light and Ranged Heavy nothing really holds you back (from a character building perspective) from going with the higher damage weapons. If you're willing to invest in a Weapon Sling, even a Brawn 2 character isn't prohibited from using a Heavy Blaster Rifle (yay Autofire!) because of the Cumbersome rating. I mean, if you had a choice between a weapon group that deals 5-7 base damage vs 9-11, which would you choose?
The problem, of course, is that the Blaster Pistol is an iconic weapon that's ubiquitous in a galaxy far, far away. Are you really gimping yourself by choosing to go the Ranged Light route "for roleplay?"
Even putting aside the fact that some characters might have Ranged Light as a career skill but not Ranged Heavy, the answer isn't so clear-cut. While dedicated ranged combat specialists are probably better off with training Ranged Heavy, light weapons do have their own advantages.
The strengths of heavy weapons are obvious; they deal higher base damage, they have superior range, and the best have neat qualities like Auto-Fire.
One of the most readily apparent advantages of blaster pistols, however, is that you can wield 2 of them. You'll sacrifice a bit of accuracy (don't forget that an extra purple die might cancel out a point of damage by reducing uncancelled successes, or an Advantage!) but you're probably at shorter range anyways so this might be a wash. This allows you to spend 2 Advantage to get a second shot in, even if you have to spread your bonus damage between the two hits. Essentially what you get is the base damage from your second weapon. Against typical enemies with soak of 3-4 this puts you on pretty even footing damage-wise with heavy weapons (assuming a lack of Auto-fire), though obviously against high soak enemies the extra damage from your second shot will result in fewer wounds. Point being, dual-wielding can mitigate the damage gap between light and heavy weapons somewhat.
Then there's the corner cases where having a free hand might come in handy. Keep a blaster in one hand and a melee weapon in the other for combat flexibility. Given that drawing/stowing a weapon counts as a Maneuver, this will usually directly translate into a mechanical advantage ("hey, I can actually Aim or take up a Guarded Stance even though my Engagement status has changed!"). Pilot a speeder bike or a landspeeder while shooting at someone with your pistol. Shoot at someone while halfway up a cliff face or a ladder. Play the game long enough, and situations like this are bound to come up.
Also worth noting is that grenades are based on your Ranged Light skill. This is probably the biggest balancing factor between the two skills, especially if you're flush with enough cash to end up with thermal detonators. Even your basic Stun Grenade can be a pretty powerful tool, though, and anyone who chooses blaster pistols over rifles and carbines would do well to keep them in mind. Just imagine the crazy narrative antics you could get away with when you roll tons of Advantage (or a Triumph!) with a GRENADE!
Finally, there's an often-neglected story-based disadvantage to heavy weapons that really SHOULD be taken into consideration at least every once in a while: they might not be welcome in public (or in the local Hutt's palace, etc.). Light weapons can be concealed, and won't draw any attention when you're walking down a city street. In most civilized areas, walking around with a rifle slung on your back is probably going to be frowned upon, if not outright illegal. Putting yourself in a position to attract Imperial attention will usually run counter to the party's objectives.
After putting some thought into it I don't feel bad about the idea of favoring light weapons, even from a character optimization standpoint. The two ranged weapon skills are actually balanced fairly well even if they occupy different niches (as they should). It's tough to make a direct comparison, but it's clear that the comparison goes beyond the raw stats of the individual weapons.