So I have an assortment of heroes and wanted opinions as to who you think I should level.
5* - Hel, Obaken, Kunchen, khiona, Domitia, Elkanen, Elena.
4* - Gretel, wu kong, Sonya, bold tusk, rigard, Li Xiu, sabina, wilbur, lil john, Grimm, triton, gormek, scarlett, kelile, colen, boril, kiril, chao, sumitomo… I probably have a few more skittleskull etc… any advice would be very much appreciated 
It depends what you have in your teams and what you are short of. In my opinion if you need healers at 4* it’s Boldtusk and Kiril and Rigard. If it’s for Titan scores and raids then Wu Kong and Wilbur. Sonya is a good attack buff and Gormek / Grimm good defence buff. And Colen, Li Xiu and Little John are ok attack all hitters
What are the 4* ascension mats that you have?
If lacking, just go for some of the 4* the rest would advise you.
Hel is 3.63, wu is 4.60, Sonya is 4.42, bold is 4.39, I think I may level wilbur next… khiona is 3.37… focused a lot on my 5* but they can’t ascend again yet so I’ll focus on my 4s for now… bit backwards I know 
I think the best is to have about 3 rainbow team of fully ascended 4 * heroes (AW require 6 team) before moving on to 5 *.
It take ages to acquire those AM for 5 * heroes.
By the time you have have a strong foundation of 4 * heroes, you will probably acquired a sufficient AM for ascending 5 * heroes.
Yeah if you’re lacking the ascension mats, then I agree that leveling your Epic heroes should be your main focus.
Well on your way to maxing:
Wu Kong, Sonya, Boldtusk 
you’ve also got Hel and Khiona at ascension 3. They’ll be there for a bit.
For your defense team now, I would do:
Wu Kong | Hel | Boldtusk | Khiona | Sonya
That should keep you around low platinum raid tier, so you can open your raid chest with platinum odds.
Here’s some good Epic heroes to focus on based on your roster right now:
Purple: Rigard first, then Sabina
Yellow: finish Wu Kong, then Gretel
Blue: finish Sonya, then do Grimm
Green: Little John, then Skittleskull (unless you get someone better by then)
Red: finish Boldtusk, then Wilbur
Little John may seem like a controversial choice, but his attack stat is really high which makes him good against titans, and his skill is deadly when it fires; -64% mana generation brings a very fast hero from needing 6.5 tiles to 18 tiles, which is slower than a very slow hero. It’s a crippling effect that can be pretty devastating in offensive raids.
Thank you for your response. It’s exactly what I was looking for 
I keep getting knocked from platinum at the moment and flip flopping so I’ll switch it up and hopefully stay at platinum!