I have given a good try out to LTP, Fila, Lithofin, and Universeal in the last 7 years.
LTP - Grimex causes me headaches, and some of their sealers simply don't seem to work (grout sealer especially). But I like their emulsifiers, and accessories.
Fila - My favourite product for cleaning, sealing and polishing, and has fumes I can cope with! I understand their thinking better than with other companies, but a 3 stage seal/polish for stone is more than many customers are prepared for. Had some issues getting reliable stocks but now reached a good arrangement with local Mandarin Stone, and get Fila products at discounted prices.
Lithofin - I believe they may be as good as Fila, but had difficulties sourcing products I need to clean and seal. My favourite cleaner (Wexa) is not even stocked by many outlets.
Universeal - I really liked their products when first introduced a few years ago. Unfortunately a severe lack of support makes it extremely difficult to source reliable supplies.
Interesting that this thread started with HG being recommended. I don't tend to use their products because they are marketed and supported like CIF and that's not a good basis for professional usage (imho).