Not really too much to add here. John C and Cranetools really said it all. The question I ask is are you thinking of purchasing a crawler? There are ups and downs to crawlers, but if your thinking of a conventional ( crawler ) vs full hydrualic truck crane or picker. The question really is how long is this crane going to sit in one spot for your work? If the answer is, not long, Id say dont go with a crawler. Because as was said above there is alot of wear and tear in walking these machines accessively. Also with conventionals, they never work harder in their service life than when lifting the booms off the ground. If one plans on doing this on a regular basis, also plan on changing alot of boom hoist cable, boom hoists, pendant lines, and sockets alike. Now Im not against a crawler, to me a crane is a crane, but there are better rigs for certain jobs.
Now Im not sure if I went the right direction here, Im just guessing that someone is looking to buy.