Arrow Multi-Looper

Arrow's Multi Loopers burst onto the scene with the triple onsalught of Viper at Magic Mountain, Shockwave at Great America and Great American Scream Machine at Great Adventure.  The rides still thrill today if you are looking for some 80's nostalgia.  Though old, these rides seem to have embodied the spirit of the steel rollercoaster and often appear in movies and tv adverts today.  They all offer similar layouts with slight differences between them, all containing a massive first drop, three vertical loops, a Boomerang (Kamikaze Curve), and two corkscrews.  The rides are generally considered rough by today's standards.  One of the three, Shockwave at Six Flags Great America, was removed in 2003 to make room for Superman: Ultimate Flight.  Although hopes were that the classic ride would be refurbished and rebuilt at another park, after spending a year in storage, Shockwave was finally scrapped in 2004.

 B&M Mega Looper (Sit Down)

B&M's Mega Loopers are the smoothest, most reliable, and most intense coasters around. 

 Intamin Mega Looper

Intamin's Mega Looper always existed alongside B&M's, ever since Monte Makaya was built with 8 inversions (taking a joint record for most inversions in a single coaster with B&M's Dragon Khan for many years).  However, the ride being part of an obscure park in Brazil, very few people rode it or knew about it.  Recognition came with Thorpe Park's Colossus, which opened in 2002 with 10 inversions (a world record to this date), and the ride proved to be a fantastic alternative to B&M, providing a much rawer experience and featuring four consequtive inline twists.

Vekoma Multi-Looper

Vekoma's version of the Multi-Looper is mediocre at best.  The rides, while offering unique layouts and elements (such as the double-inverting Butterfly), are some of the most painful rides in the coaster industry.  Few were ever built, and the most famous example is probably Goudurix at Parc Asterix in France.