M4 is the best pipe vs. price that you can buy. i bought mine (one in Tersejr. test on yfztech.com) for less than $400 dollars as a full system and it performed flausly. lol i sold it super cheap too cause no-one knew what they were. lol
my opinion of what works good
M4, jardine, Nmotion, Sparks BC, and esr.