I assume you're talking in game normal buyable cars not mods? (as you've tagged it pc)
Fastest bike around most tracks is the Shotaro
Fastest top speed bike is apparently the bati 801 even tho it used to be the Hakuchou.
Fastest car around a track is the RE7B but it's closely followed by the Tempesta which is a lot cheaper and a lot easier to drive
Fastest top speed car is technically the 900r but you'll not really ever get there as it takes too long. So go for the 811
Best all round car is probably the Nero custom for racing and the T20 for free roam