@Buccaneer:
Well, this is just from what we've seen. But I don't think it's the weapons that make him unique, but his fighting style. He seems to take people by suprise and appreciate set ups, like blowing fire at people to confuse them or straddling with Centaur. I'd say he's most like Krieg, but has his own kinda flair.
I have to wonder how effective such a unique style will be from a storyline standpoint during a more dramatic battle. Sure, they worked during the Nero fight and will be hilarious during the current bout with Fukurou, but how does Franky work if he ever has to go into a battle with a serious character?
He'll have to resort to some of his more mundane attacks, which are those that pretty much duplicate Luffy's and Usopp's.
@leokeren:
4. strawhat needs a good carpenter. while tom's worker is one of the best in the island, it is IF THEY WORK AS A TEAM! paulie alone can't do a thing. In contrast, franky had always made ships alone, ever since he was young.
See, this is another thing that I'm not sold on for this reason:
The rest of the crew, while incredibly skilled at their respective roles, are nowhere near the top of their fields. They'll be at the top by the time the series ends, but that's still an incredibly long way off.
How does Franky develop? He's almost at the top anyway, so it's not like he has to go on some amazing voyage around the world to master his craft like the rest of the crew.
His goal is to build a ship capable of sailing to the end of the world, not that he sail with it. His goal doesn't require that he leave Water 7 and neither does building the ship for the future Pirate King as Tom built the Oro Jackson without accompanying Roger.
The rest of the Straw Hats all have goals that require them to sail the world and improve their skills in their fields. Barring Franky building them a temporary ship and then rebuilding another one later, how does he accomplish either as a Straw Hat?
Oda may do just that, but I'm not sure I like the sound of them switching ships again down the road. It's hard enough to believe that he could ever replace Merry, but adding another ship down the road is only going to remind us more of the ship that they used to have. It's best that the first half of the series be with the Merry and the second with her replacement as we're never going to get used to a new ship otherwise.
At this point, Franky seems much more likely to join, but there's a wealth of potential in Paulie that simply doesn't exist in Franky.