I am entirely biased toward nightblades, but I have all classes and resource variants. Maybe some notes will help you pick. I’ll lost in order of my preference, top down.

Stamblade (khajiit is my favorite, Redguard and wood elves work too): the pros here are stealth and massive damage. Con, they are squishy. And they require really learning the game mechanics...new players will feel defenseless, then if they pay attention and start to realize “oh, this skill plus this skill adds this,” then things will click and the blade will be fun and powerful.

My main is a stamblade, and I’ve stuck with him because I find the class versatile and really fun. I love their class skill lines, and also the physical weapon skill lines. I run him as a ranged bow build at times, or a melee ninja, or an all-out dps powerhouse. He’s fast and can stealth past any battles I want to bypass. This will absolutely be a harder class to learn, but I always tell new players that if you start with a NB and learn it you can switch to an alt of any class and succeed...you’ll really learn how to play the game.

Magplar (high elf, Breton): the pro here is immense survivability and decent resource management. The con is that dps can be a bit of a challenge, though they hold their own. I use my Magplar for VMSA, and he’s way fun.

A magic Templar is a very in-your-face fighter, which feels sort of unique for a magic toon. I really love their class skills. To be honest I’m not a huge fan of the magic weapon skills lines...there are some ok skills, but they feel a little monotonous to me. A Magplar has endless heals, so a lot of players start here. You’ll rarely die. I think starting Magplar makes people addicted to heals, lol, and a lot of Templar players have a hard time adapting to other classes.

Magblade: I don’t know...this might tie with Magplar for me. They’re really fun. Pro is stealth and great aoe potential, con is the squishiness again. They play a lot like i describe stamblades, and most of the best nightblade skills have both stam and magic options. You will be able to fly through the game in endless stealth when you want. And they can put out some sick damage when played right.

Stamplar: pros are fantastic resource return and a good blend of class skills, con is that dps can be a challenge and they have no ideal execute (which I think is lame). I want stamplars to be more fun and higher on the list, but Imfijd when I want to play stam I go for my stamblade and stam sorc over my Templar. I think it’s because I solo a lot, and the lack of power frustrates me. Stamplars have a skill called repentance, which returns stam and health from dead bodies. In more group play this becomes immensely valuable.

Honorable mention: stam sorc. I love my khajiit stam sorc, which to me is a good compromise between blade and Templar. My stam sorc gets very good dps, slightly,less than my blade, but he is almost as tanky as my Templar.

Overall I might suggest you roll a couple of characters and experiment...you get eight slots, after all. If you abandon a character they can be a crafter or mule. One note I’d make if you try a few toons is that the different classes can come into their own at different levels. A magic Templar opens a lot of their core skills early on...you’ll have a pretty good sense of how they play by level 20. From that list...hmm...stamblades are the slowest to develop. A lot of their skills start off as magic variants and feel clunky, then they have some good skills that open really late. A stamblade will evolve in how they play all the way to vet.

Let us know what you pick, and have fun.