John this is a very common question, if you use the search facility and look for NEWBIE or HELP you will find loads of advice, most of which advise taking some formal training before buying a machine. I went on the NCCA coarse for about £300 they showed me a range of SYSTEMS (not manufacturers) so i could choose for myself, i had allready bought a truckmount but have since bought a rotary and a dry compound system, the knowledge i gained on this course was essential for explaining how these systems worked and what their benefits were.
Hope this helps
Dene