I like Sendars the most, though Drasnians are a close second.
Sendars are calm, practical and down-to-earth farmer types - I just feel like I'd want to live in a country like that. Durnik is my favorite character (I love him the way he is, just like Polgara does) and he's a stereotypical Sendar, so... yeah.
I love the world Eddings created, but I don't think creating nuanced, original cultures was his strong point. Looking at his map is like looking at a map of Western Europe after too many beers. That said I still remember them after many years, which says a lot!
I guess I am talking about the countries as a whole rather than the "races" but obviously the two overlap.
Sendaria- has a more interesting back story and has evolved unlike the older countries.
Algaria- remind people of the Mongols, but part of the "Germanic" Alorn group. I liked the idea of their huge citadel which, unbeknown to their enemies is usually empty.
Cthol Murgos- I thought this was one of the more nuanced and interesting countries, I was intrigued by the huge unexplored country divided into military districts. I liked the idea of the separate caste of priests (Grolims IIRC) with their own stronghold. I think the Grolims may have been in all the Angarak countires, but remember most vividly the bits about Cthol Murgos.
Arendia- A pastiche of high middle ages, complete with pompous faux-antique dialect. Chivalrous and stupid Knights in shining armour or plucky robin hood types? Take your pick
Cherek- Viking barbarians. Yawn.
Tolnedra- Referred to as an Empire and obviously modelled to an extent on Rome, however seems to be more or less just an ethnic homeland like most of the other countries, rather than an empire.
I seem to remember they had soldiers stationed in Sendaria and Arendia in a mostly friendly occupation, which is more "empire like" behaviour and a young Garion being a little uneasy about this. I guess it would have been interesting to expand on this a bit more and the social/cultural/political issues of it.