Macfa1,
When buying any crane, the first thing you should prepare is a hook map. That is, determine how much weight you will lift at what radius from the center of boom rotation, and how often each weight will be lifted. What you will probably find is that 80% of your lifts will be at 10 Tons or less but at radii of 20 meters or more. The decision point will be how much you want to spend to cover the very infrequent lifts.
Based on your hook map, shop for a crane by reviewing the manufacturer's load chart. A 50 Ton mobile crane from one manufacturer does equal a 50 Ton mobile crane from another. They may have significantly different load charts. When reviewing manufacturer's load charts, also look at how many charts are involved. Some manufacturers require additional counterweights to achieve rated capacity and may have severely restricted capacity when not lifting over the front or rear of the crane.
Another factor to consider is clearance. The bodies of mobile cranes vary greatly, although there is a significant trade off between wheel base and stability. To ensure stability, buy as large a piece of equipment as your facility can allow.
I hesitate to recommend a single manufacturer, there are many and varied options, but mobile crane operators seem partial to Demag (Terex), Linkbelt and Grove. Kato, a Japanese manufacturer makes a beautiful machine for a reasonable price. All have excellent web sites with pictures and generic load charts.
Good luck.
