I've been trying to give this a lot of thought, but I can't come to a conclusion. I've played every race for at least one playthrough, and love them all for different reasons. I'll give a couple of pros/cons for each race and see if it helps me or others make a decision.
Altmer -
I love these guys' magical ability and their air of grace, and there's a lot of mystery about their recent history and room for interesting backstories. Their size makes them imposing warriors which can be even more intimidating when using magic along with steel.
Their airs and graces do sometimes make them feel a little cold and tough to connect with, though, and it's tough to RP an Altmer from Alinor due to lack of current lore on the area, so choices can be limited to growing up or living elsewhere. A lot of people seem to find it difficult to distance them from the Thalmor in one way or another (either being a member/ex-member or having some family tragedy related to them).
Argonian -
Members and characters of mine of this race often have an interesting sinister mystery about them. Due to this they make great rogues and assassins, especially with their skills, but also make great warriors or mages. I love their history and their quiet ambition, particularly against the Dunmer and Argonians have been some of my most interesting characters to play and write about.
The tail. I have found a mod which hides tails on the beast races. I shall have it. Also, they're a little conspicuous in the bright nights of Skyrim, especially when passing by guards in walled cities. "The Argonian did it" doesn't leave a character with much room to blend in and slip away. But darker nights is another thing that can be modified, when PC time comes.
Bosmer -
I'm a big fan of archery, and Bosmer can really give you that David v Goliath feeling when you take down a group of big bandits plated in armour. They also make really good nightblades, too, if you choose to ignore archery for roleplay or backstory reasons. They can blend into a crowd well yet still maintain that feeling of being in an unfamiliar land, which can be really valuable for character interaction. Also, the Green Pact stuff is a really interesting topic for Bosmer characters to have a take on.
The lack of height is part of their character, but I'm fairly tall and find it hard to play a short character. When I take the time to really RP one though, I don't think it'll bother me like it has in the past.
Breton -
These guys can do so much, and I often choose them for my more unusual builds, eg witch-hunters, priests, etc. I really like their intelligence and scope for different characters, though, and they also make pretty convincing Dovahkiin. The magic resist stuff is pretty useful, too. They also seem to be closest to Brits, with a lot of Breton NPCs being voiced be Englishmen. The connection with the Reachmen is interesting, too.
Again, these guys are tiny, so the tall, dark and handsome rogues that I'd like to play as a Breton can be tough (although - it'll be something I can remedy with showracemenu
)
Dunmer -
Similar to Bretons in that they are so versatile, in fact probably the most versatile, and Dunmer are probably one of the more straight-up badass races. Capable of being high-powered battlemages, or deadly assassins they offer a range of options well-suited to them. They've got a great history, too, which allows for some really interesting backstory development. There's also an interesting side story with their plight following the eruption, and their situation in Windhelm.
I'm always tempted to make evil characters with Dunmer, but I've made good ones in the past. One of my only issues with these guys is that I struggle to choose how I want to play them!
Imperial -
Again, versatility is one of my favourite characteristics when thinking of Imperials. One of my favourite characters, and one I always have saved, is an Imperial rogue, with archery, one-handed, sneak, block, light armour and speech, but I've played more Imperials than I could count. They make decent Dovahkiin, too, and have a lot of history and lore for us to create interesting characters with.
They can be a little... mehh, at times. That's my only complaint.
Khajiit -
This one loves Khajiit. Intelligent, mysterious, stealthy, they make excellent thieves and bandits, and I still remember really regretting deleting my first Khajiit, a black level 47 badass in Nightingale gear, roughly two years ago. I love how they're capable of being jolly and carefree, or dark and sinister.
Again, the tail. I also find it quite hard to RP Khajiit because they are so different. The whole 'are Khajiit allowed in cities' thing weighs on my mind at times, too, so I tend to only have them play in unwalled cities unless I have a reason for them to be allowed in.
Nord -
Skyrim is my first TES game, so I obviously have a soft spot for these oafs. I really like the history and variety in this race, and the game provides so many sources of information and inspiration to create a really interesting character (or 20). I've played more Nords than anything else, probably more than Khajiit, Bosmer and Argonian put together, but I love them. They resonate with a lot of my approaches, and remind me of my dad's quite traditional views on honour and respect.
I can't really think of any negatives for Nords. There is something for everyone with these guys, with Skyrim being their home province. I'd probably have to name Nords my favourite.
Orsimer -
I love these badasses. There are no finer warriors or barbarians in the game, but they lend themselves well to other styles, too. I once had a great deal of fun with an Orc assassin, who used a hammer and Berserker Rage to bludgeon targets to death from stealth. Now
that was a mean dude. I like to play Orc paladins, too, and give them a sense of honour and righteousness, which is fun when you're playing a kill-happy race. They're really great for revenge stories, too.
It's easy to pigeonhole this race into playing warriors, and I sometimes find it hard to really get into a RP with an Orc that's not a stabber, slasher or crusher in one way or another.
Redguard -
Again, very interesting history and culture, with lots of scope for backstory and RPing. I love sword combat, so this suits playing a Redguard perfectly, as well as their willingness to use certain magic. Unarmoured swordsmen are my chosen playstyle for this race, which I really enjoy.
The only downside I see with Redguards are that they are, like the Imperials, a little boring. There aren't many Redguards in the game with real character or anything particularly interesting to say. Isran is one of the more interesting Redguards, but he plays a fairly generic role.
Following this, I'm going to vote Nord.