First, consider the size and capabilities you need. Was your old rig big enough to do the work, or do you need more power? Don't be fooled into thinking that bigger always is better. Too big a rig will make some locations inaccessible or require a lot of winching, plywood and site restoration. Too small, and you'll have to “run it up in the curve” so far that it will wear out quickly. Is it time to make the change from a kelly rig to a tophead? If so, bear in mind that these two types of rig drill differently and take a little getting used to. There always is a learning curve to a new rig, and major changes in rig type tend to steepen this curve. Each rig does some things better and some things worse than the other; it's just a matter of playing to the strengths of the design.