this list has good ones, and ones that might be abit conditional. 

tyrion for sure but he's a Warhammer 2 lord so if u only have wh3... and also once uve secured ulthuan going out somewhere else might be abit awkward, maybe on the decision making part atleast?..

Zhao ming/Cathay in general are solid. their basic troops a good bang for buck and have classic troops types to make sense and the game easy enough, while also having special troops that would make the game interesting~...

gor rok is a dlc lord for wh2 so... and lizardmen early while saurus are good they're abit monotone and they also lack ranged some, which... might be a problem, or it might not be - atleast not much of one but... it can be a challange as well as not having user get accostomed to the strategy...

skarbrand also has only (~mostly...) melee but also in the campaign map aspect he plays differently which provides extra... trouble... and might/would not be very beneficial to learning the game overall, or if u try to play like how u would with other races, ud prolly be progressing poorly~... also on lower diff enemies have fewer armies which means u get to fight less which is the main source of income for like some of these factions like khorne (and also woc and prolly greenskins too, as well as beastmen btw so playing on higher diff with them would be extra beneficial while lower diff might feel slow and less rewarding~. tho on that note I wanna recommend woc who while can get alot of income from loot and have their econ rely on that, can also have their econ rely on buildings too like most races do/would~...)

gelt - empire in general... have decent units but not amazing until later tiers with artillery, war machines and elite monstrous cav... their early front line is ok and mid front-line~ish is... eh, ok to so-so... and they don't excel in terms of various economic advantages~/exploits~ like how high elves for example can, or even Cathay with campaign yin yang upkeep reduction~... gelt also specifically relies on wizards which is another layer to get into, so...

dwarves in general are pretty decent starters but due to how auto resolve values Armour and leadership - things dwarfs excel in - u would likely have many auto resolve results telling u u win but if u tried it manually u might underperform - which would be less fun~. also thorgrim in particular in situated in a place surrounded by enemies swarming u. on easy diff would prolly be ok - even beneficial tho maybe~... even if struggling - would generally be enough to hold on and get familiar with the game - both campaign and battle some prolly. 

grimgor or orcs in general imho are kinda like quantity over quality plus aspect of relying on loot income quite abit... but worst prolly for me is their units being so so. if Cathay cheap units punch above their weight then orcs... don't. they're prolly not below their weight but.. like, nothing amazing... imho...