hi im new to this but id like to see peoples opinions on which is the best weapon ordnance in fallout 3, including explosives, pistols and heavy weapons.

If I had to choose one of those, then Lincoln's repeater. However, I prefer these:

Unarmed: Bare fists
Melee: Shishkebab
Guns: Perforator or Xuanlong, depending on whether or not you are a sneaky character
Guns (1 handed): Sydney's SMG
EW: Metal Blaster (outside VATS) or A3-21
BG: Vengeance
Explosives: Nuka Grenade (mines are nice too)

A3-21's plasma rifle for me. Despite ever gun that came out in the dlc's it was always the work horse of my arsenal.

terrible shotgun takes the fear factor out of feral ghouls

Wazer Wofle, the Terrible Shotgun, and the Inflitrator.

i like a good old fashioned combat shotgun. shoot them right in the face at close range.

Spiked Knuckles
Blackhawk
Eugene

Really, "best" depends on your playstyle.
The dart gun is a strong contender for making Deathclaws easy to kill with a BB gun.