I use an i1 Display Pro colorimeter with i1 Profiler software for my two main monitors (one used in the studio, tethered, and one for editing), and a DTP94 with ColorEyes for the softproof monitor. I used to use an i1 Pro spectrophotometer for the main displays, but switched to the Display Pro. A good colorimeter may be better than a spectrophotometer for the darker values on your screen because a spectrophotometer loses accuracy in low light levels. We recalibrate every two weeks. The i1 Display Pro with I1 Profiler will do real-time profile correction for changes in ambient light, if you need it.
The i1 Pro has been superseded by the i1 Pro 2, which I would strongly recommend over the i1 Pro if you are considering a single instrument for both display and printer.