One of Conn's more noticeable improvements over the years has been the adoption of rotary valves in their trombone designs. The purpose of these valve attachments is to improve the trombone's range and the variety of slide positions you can use. There have been a few different valves developed, but the most common is the single rotary style found on instruments like the Conn 88HO Symphony Series F Attachment Trombone and the 52H Artist Series Trombone. Others, such as the 112H Double Rotor Bass Trombone, have two rotors, stretching their range even further.
Of course, if you would prefer a classic trombone with no rotors at all, Conn has fantastic options including the 8H Symphony Series Trombone and 100H Artist Series Trombone. You may notice that the 8H has a rose brass bell, while the 100H has a yellow brass bell. Both bell materials are well-represented in the Conn lineup, and choosing between them will be one factor in your decision. All other traits being equal, you can expect a warmer sound from rose brass and a lighter sound from yellow... but keep in mind that bell shape makes a difference too, so be sure to factor everything in before settling on your favorite.
With everything taken into account, you'll find it surprisingly easy to narrow down this selection to the instrument that's right for you. Pick your desired style, rotor layout, bell shape and materials, and you'll quickly arrive at the perfect Conn trombone to match your exact specifications. After that, all that's left is to get ready to play it.