I'm really glad you asked this question, as I just came across this same dilemma, as of yesterday, with Atton (one of my main team members).
Dual Blaster Pistols would certainly be the stronger choice in the end, but the single Blaster is more aesthetically appealing and seems more sensible in a roleplay. I think of dual pistols as more of a Bounty Hunter type of thing, which certainly doesn't resonate with my one-time-Scoundrel-now-Jedi Atton.
I ran a small test between the two on Nar-Shaddaa, in having him test out both options with Master Speed and Master Rapid Shot, while also equipped with Level 4 Precise Shot.
The Pistols, on average, did 10-12 more damage than the rifle did. But there are a couple of problems involved: Neither of the two weapons were particularly upgraded well - the pistols maybe even to a lesser degree. Meanwhile, Atton is automatically equipped with Wep Specialization Pistol but did not have Wep Specialization Rifle, so I don't know how much of a difference that made either.
Ultimately, I think I'll base my own decision on how much stronger dual-wielding is in comparison. If the difference is minimal, I'll go with aesthetics. If it's huge, I feel more inclined to buck up and go with the dual-wielding.
So if anyone can post up, say, max/average damage with a strong Rifle vs max/average damage with equally upgraded/strong pistols, I would very much appreciate that.