What is the difference between 4D Vaser lipo, 3D Vaser lipo and just Vaser lipo?

VASER is VASER. It is a technology that disrupts fat from its surrounding structures to allow it to be removed easier with liposuction. 3D/4D/etc. are all marketing ploys and nothing more. Virtually all VASER surgeons will do fat transfers along with VASER which is where they market as 3D/4D and the like. I would encourage you not be duped by surgeons whose marketing seems to be more impressive than their results. 

VASER is VASER there is nothign else. its a device used to get better contouring and skin retraction AND IT DOES THAT if you know what you are doing. its best to combine it with renuvion IMO, as Ive done 1000s of cases and have results unlike most.  those who say otherwise either dont use the devices or dont know how. with that said, all the terms are just marketing. you need someone who is experienced in advanced contouring and uses energy based devices to get more than a "traditional" Improvement (see links).
You need a formal evaluation by an expert in body shaping and contouring to determine what is best.  Traditional liposuction awake and smart liposuction are old methods and do very poorly for tightening skin or significant skin tightening or contouring.  Small problem areas can be improved slightly by these methods.  The best in body contouring not only removes fat with energy devices like VASER ultrasound but also internally heat the skin with radio-frequency devices such as J PLASMA/RENUVION, InMode BodyTite, ThermiRF to heat the under surface of the skin and tighten it at the same time as fat removal. These combinations are called 4D HIDEF VASER contouring and can only be done by a well . trained body contouring specialist. At the same time fat should be harvested, PRP and stem cells added and injected into muscles or indentations/cellulite to get body shaping and contouring.  This is known as a Brazilian butt lift when you inject the fat to the buttock for contouring and lifting, but fat can also be used in areas such as the chest/breast, arms/shoulders, calves and face.  Cellulite should also be treated with cellfina, sculptra, subcision and/or fillers such as bellafill, renuva synthetic fat, or sculptra.  If skin is very loose before surgery then it will need to be removed such as lower abdominal skin (tummy tuck/abdominoplasty), breast skin (breast lift), arm skin (brachioplasty).  Overall you need a full assessment, but simple liposuction alone will not tighten skin and needs a combination of various methods -- fat removal, skin tightening, defining, fat grafting, skin removal -- to get the best in body contouring and body sculpting.  Dr. Emer.

There is no difference between the three. The Gold Standard for superior liposuction results requires use of the advanced technology of ultrasound assisted VASER liposuction. As an official trainer of VASER liposuction, I perform full body liposuction cases every week. VASER liposuction has been the only modality that has consistently resulted in outstanding liposuction outcomes. VASER liposuction ensures a smooth contour regardless of degree of excess fat by virtue of being able to remove any and all remaining fat comprehensively and uniformly. If skin redundancy is observed, Renuvion technology can be simultaneously applied to tighten your skin to optimize your overall contour outcome. A Skype or FaceTime consultation with a VASER specialist will help you get an accurate recommendation and pricing.
Respectfully, 
Arian Mowlavi MD, FACS
Realself 100 Hall of Fame Inductee