I use Alfa A or Hifi, depending on the time of year.
Countrywide own brand H&P cubes.
Trident sugar beet pellets.
Oats straight from a farm.
Cal-Mag and Herbal Shine Extra from Natural Horse Supplies and NAF Electrosalts when needed.
Can't really say I have a favourite product.
ETA - I say I don't have a favourite because I just try to use what is best value - I think a lot of expensive products are unnecessary or have a cheaper alternative.
I don't stick to one particular brand - just use what is best for the individual horse at any particular time. Currently using Spiller's Response Slow Release Energy Cubes and Speedibeet, but have also used Dodson & Horrell Staypower Cubes, Allen & Page Fast Fibre, and Bailey's Everyday High Fibre Cubes over the last 12 months.
At the moment Chestnut Horse feeds Alpha, there sugarbeet & Alpha Easy or lite but they have been on some of them have been on dobson & horrel high fibre cubes before or allen & page calm & condition.
I like to use Spillers where possible- and Dengie for Alfalfa:
Spillers Happy Hoof and Spillers Grow and Win (For youngster)
Spillers Slow Release Cubes
Spillers Conditioning Cubes (just to top dress their feeds if needed)
Dengie Alfa-A Oil
And Supps -where needed- include Cortaflex, Pink Powder, Magnitude Garlic granules (or NAF Mint & Garlic depoending on whats avail), Linseed Oil, NAF Biotin- they don't all need all of that lot though!
Love the Top Spec range after my lad was so poorly with peritonitis. Also like Allen and Page, Dengie products and absolutely love Readigrass. I could sniff it all day