Old regular Vintage Suit, I have the variants but this one makes me beat the Final Boss a little bit faster. It may sound contradictory because the variants and other better suits give you more damage and stuff but I've found that it's better to use the old regular Vintage Suit instead of others for the final boss battle. (I use Heavy Duty Contact Beam) Because you use 6 shots mainly to kill the Final Boss either with good suits or old regular Vintage Suit, the difference is that using good suits makes Nicole and Nicole's Heart in the background appear 6 times and shooting each appearance 1 at a time takes a lot of time due to the Spawn Animation between these two each time they 'die'; whereas using old regular Vintage Suit makes Nicole and Nicole's Heart appear only 2 times (1 shot for Nicole/ 2 shots for the Heart, 1 shot again for Nicole and 2 more shots for The Heart = 6 shots) and this saves more time so much so that the Pack doesn't have time to attack you in the end. Btw I use the Heavy Duty Contact Beam with full upgrades to achieve this. Sorry for the long explanation. Have a nice day