What is the best injectable filler to use on thighs to create volume and fill large indentations?

A long lasting filler like bellafil would be my choice. It is off label use of course, but better still is fat transfer which is less expensive and more lasting. 

For unique cases where a variety of modalities could be used to treat the condition, I would suggest an in person or virtual consultation to develop a custom and effective treatment plan. It is difficult to precisely define the best option without collecting the same information. I suggest reaching out to an expert for a consultation with surgical and non-surgical methods to get a comprehensive option. Best, Dr. Emer.

Fillers can certainly be used to help correct the defects but you will need a lot of product. If you don't have enough fat to use for a transfer, I would use a more permanent product. I like to use Bellafill and combine it with PRP to maximize the formation of your own collagen to fill the defects. This way you will not have to keep repeating the procedure every year.

I have treated many patients with indentations from liposuction or removal of moles that have left scars.  The best treatment for these types of scars is Juvederm Ultra Plus.  It lasts longer than most fillers and has no side effects.  Please consult an expert in cosmetic scar revision and fillers for the best results.  Best, Dr. Green

I'm sorry to hear about your unfortunate experience. Autologous fat is still the best to treat indents that may have been caused by poorly performed liposuction. If you don't have fat at all available, I would use Sculptra as the next best choice. You still need to see a plastic surgeon who's well-versed with such techniques. Good luck from New York City