I'm going to vote for Guars, simply because I think they are awesome, were in my favourite game in the series and my Dunmer alt felt odd riding on a horse; although my khajiit alt appreciates having a true mount from Elsweyr and being part of a coordinated roaring chorus is always fun, so I do like also having a senche.

The flaming horse, well, does look somewhat striking, but I'll pass: the costs to store it in a stable must be exorbitant with its tendency to set them on fire by accident.