I'm going to try and make a character who doesn't get involved in fights so much and instead talks his way into and out of things. However, the creatures of the wasteland can't be communicated with so I need some skill in either guns, melee weapons, laser weapons or unarmed.

I was thinking that either guns or melee weapons would suit my smooth-talking guy as either pistols or knives would suit him well but not too sure. What do you think?

Don't train any skill. Just get a riot shotgun and load it with beanbag rounds that lower fatigue. You can just knock everyone out and run away. Or you could just use regular rounds on the shotgun and blow everybody's heads off. :gun:

I'd say guns.
Energy Weapons are too weak (as a non dedicated guy), Melee weapons/Unarmed require point blank range and explosive come with the risk of blowing yourselves up.

If you go ernergy, you will be able to keep your STR very low compared to going melee or even guns for that matter. Since a peaceful character won't use much ammo, a weapon that is ammo-intensive is not a problem.

Multiplas Rifle (plasma shotgun) requires 50 energy, STR of 4 and can do up to 1000 damage in a sneak crit. All you need. Compared to Multiplas, Riot needs STR of 7 and 100 Guns - and does less damage.

I wouldn't say my character is a pacifist, he'll do things that result in the death of people. He's just not one for combat himself. Preffering diplomacy and being a sneak to get things done

You could always just make your companion(s) do the dirty work.
I believe high Charisma results in more powerful companions.
And there's the Ferocious Loyalty perk too, which makes your companions more resilient when you're low on health, giving you the ability to run or hide while your companion finishes the job.