I use Trotter. Absolutely LOVE it, as do my horses.
Sentinel and Blue Seal are the same company, so you shouldn't have any worries about the quality regardless of which BS product you go with.
Trotter is legume, not grain, based. That makes me happy. Its main ingredient is alfalfa with added soybean hulls. Both are really good for horses, and I find the Trotter makes up for any vitamin and mineral deficiencies that might be in my hay.
Even my 26 y/o glistens, and the two younger horses are fat, happy, and healthy.