You want attitude? Oh, I know where you can find attitude! LaBella Deep Talkin' Flats on a P bass is plenty of attitude. They have that deep, authoritive thump and have a very smooth finish with a super tight wrap on the winding. I have not found DR Legend flats and Chromes to be as smooth.
If you want the classic old school thud I'd go with La Bella.
+1^
I have LaBellas on my MIA Fender P/J 5 and I find it to be, for me, an absolutely ideal combo. I didn't like Chromes my P basses, but I like them a great deal on other basses, like a fretless.
I am one of the few who does not care for TI's due to their high price and low tension.
Yes, the LaBellas can be pricier than Fender or GHS, but since you shouldn't ever need to change flats (I have a 5+ year old set of Chromes still going strong), it works out OK. I know I could say the same for the TI's, but the low tension would still be a turn off. IMHO nothing beats LaBellas on a P Bass for that classic P bass tone.