between fallout new vegas, and fallout 3, which one is better?
Pick your poison - they're both great.
Make sure you go w/ the Complete Editions on both:
That would be Fallout 3: GOTY Edition + Fallout New Vegas: Ultimate Edition.
Each of them have some meaty DLC's. For
FO3 - Point Lookout & The Pitt are great; Mothership Zeta is pretty good; and Broken Steel is pretty much essential (b/c to keep the game + game-world itself going after you beat FO3 base-game, you NEED to have this DLC period.
FO:NV has some pretty good DLC's...but the stand-out for me - and one of the best DLC's ever, IMHO - is Old World Blues. The other DLC's are all good and worth playing.
With
FO:NV - you want to go Ultimate Edition also in case you want to install JE Sawyer's Hardcore Mod (since it requires ALL DLC's). He was lead dev. on FO: NV, who made a hardcore mode even harder than FO:NV's mode b/c he felt the game was too easy for him, even at its official hardest mode + settings.
As for the base-games -
FO3 set a new fresh-ness and gold standard for how to make a FO game actually work in the modern-era, for both PC players and console gamers. FO3 when it came out looked incredible for a RPG and actually had a decent storyline for a BethSoft game. And more so than Morrowind, for a BethSoft game - there was often actual pretty good amount of decision-making and branching decisions. While they aren't the best w/ storytelling, character design, and that stuff - this was one of their best outings. The story w/ looking for your dad will tug at your heart, more so than anything. Also, the world-exploring + open-world was fantastic; and looking + exploring a basically destroyed East Coast was unforgettable.
FO:NV was developed by Obsidian. Obsidian, in the technical department for storytelling + character development - they will out-class most developers by a mile. Very few are on their level + BioWare's level for RPG's, in terms of doing this stuff extremely well. In the narrative department and the actual writing of the dialogue - it's excellent; as you'd expect w/ someone especially like Chris Avellone (Planescape Torment + Fallout 2, anyone?) + J.E. Sawyer in the group. Also, a lot of the humor from Fallout 1 + especially Fallout 2 that felt missing in BethSoft's FO3, it was in New Vegas. Also, when it comes to decision-making; decisions checking your stats + skills - Obsidian again out-classes Bethesda...by a mile. While the Inventory, gameplay, and all of that stuff might not feel as anywhere as fresh as it did in Fallout 3 - the improvements in pretty much every other regard b/c Obsidian made it also make this another great Fallout title.