If you're a legion player there are a few tier lists I like to play. Abby is always a noob friendly tier list, but you'll find it restrictive once you're past the early stages of play. It gives you a lot of advantages and tends to be melee centric which can be a problem in today's ranged heavy meta. Since Colossals I've started to reconsider her and trying to find a list I like.
The obvious choice would be eVayl Tier 4. She's amazing, her tier is outstanding and is legit. She's competitive and has a strong game. I highly recommend it later when you're more experienced as it takes some skill to use well and the full understanding of the rules to abuse
Outside of those two, there are a few others I've considered but have not tried, Rhyas's rear guard (Tier List released in No Quarter Magazine), Bethayne's tier list, but as stated above, they can be very restrictive and sometimes better to avoid altogether.
I'd advise you learn the game without tiers for now, get your rules down and find a style of play you enjoy. Learn what all of the models in our faction do, their strengths and weaknesses and then explore tier lists. Without the knowledge of what you're actually giving up in direct comparison to the benefits of the tier, it will be difficult to determine if a tier list is actually beneficial. Have fun and let us know what you find!