@Aldrich:
Let's see again the reasons why Franky could join the Strawhats:
-He's the spiritual heir to the man who build the first Pirate King's ship, there's the symbolism of him being to Luffy the new Pirate King what Tom was to Roger
Which, strictly speaking, works against him as Tom built Roger's ship without accompanying him. Otherwise, he'd have been charged with being a member of his crew rather than simply being an accessory to Roger's crime by providing him with a ship.
-He's fighting alongside the Strawhats against the CP9
Considering that Paulie's completely disappeared after Puffing Tom leaped across to the Justice Tower, we may well see him again seeing as how we checked in with the other two shipwrights.
-He's a thief with no social status and no responsabilities
Paulie just beat the hell out an elite Houbantai unit, helped hold off a bunch of Marines and CP Agents, and directly attacked three Judges. I somehow doubt that the World Government is going to turn a blind eye to his continued presence in Water 7.
He's not working for Galley-La anymore anyway, what he is doing here is strictly freelance.
-Crazy personality and fighting style
Which we've already seen quite a bit of while Paulie remains a cypher by comparison.
-He's a f*cking cyborg shipwright, would go along well with a reindeerman doctor, a long nosed lying sniper and the other weirdos of the crew
Actually, only Chopper is really that much of a freak when it comes down to it. Devil Fruits are what make Luffy and Robin weird rather than their personalities.
-Luffy's sketch
As far as the sketch goes, you could make a fair argument that Paulie fits that image as well as Franky does. His flared shirtsleeves are a good approximation of the arms, he has slicked-back hair, wears goggles, and his shirt is a better approximation of Luffy's drawing than Franky's is.
Now let's see Paulie:
-He looks cool and fights with ropes
There's no real match as far as I'm concerned.
Here's the advantages I see to Paulie:
1. He helps balance out the crew between idiots and non-idiots, Franky doesn't. He's much more level headed than Luffy, he's fairly knowledgeable about the sea itself, he's a direct counterweight to Sanji's idiocy around women, but he still a major character flaw to exploit for comedy.
2. He's a medium strength character; he's strong but not freakishly so and doesn't require a deus ex machina for him to be taken out of a fight like Franky.
3. We know next to nothing about Paulie except that he was a little kid who was wonderstruck by the Sea Train when it was built. There's a helluvalot more room for character development for him that there is Franky. Paulie's even quite a bit younger than Franky, so he still more room to grow as a person.
4. He's saved the lives of several of the Straw Hats already and there is a reasonable argument to be made that he actually cares about them as people. He could have easily been killed by the Aqua Laguna on that bridge but went out there anyway.
5. By all appearances, Luffy is on pretty good terms with Paulie, but he doesn't like Franky.