I also use an excel table that I made using the equations from github.
In an example on why I use Russian planes=
Guarulhos - Dusseldorf, ~9500km, goal of ~3500 pax/week
2x A380 -> ~1.8mi fuel cost, 0.5mi decreciation = ~$2.3mi in 4 slots, 3412 pax Initial investment of 900mi <- 674 per pax in fuel + depreciation
4x 96-400 -> ~2.05mi fuel cost, 0.13mi decreciation = ~$2.2mi in 8 slots, 3448 pax Initial investment of 200mi <- 638 per pax in fuel + depreciation
7x Dreamliner -> ~1.45mi fuel cost, 0.48mi decreciation = ~$1.9mi in 14 slots, 3500 pax Initial investment of 875mi <- 542 per pax in fuel + depreciation
3x 747-400 -> ~2.0mi fuel cost, 0.57mi decreciation = ~$2.6mi in 6 slots, 3960 pax Initial investment of 1050mi <- 656 per pax in fuel + depreciation
5x 767-300ER -> ~1.4mi fuel cost, 0.5mi decreciation = ~$1.9mi in 10 slots, 3500 pax Initial investment of 905mi <- 542 per pax in fuel + depreciation
This is NOT considering "airport fees" and "other costs" and total passenger capacity per route. Crew costs are linearly fixed and the same for all planes, so it's not relevant.
An extremely important aspect is route demand/offer, you won't be able to compete with other airlines using less efficient planes.
It's also important to consider max range and versatility (e.g, you can't use an A380 in a small airport that could maybe fit a Dreamliner)
Obviously, different routes will wield different results, longer routes will benefit more the A380 (e.g) because of speed, in the above example the A380 is 1h10min faster, and that saves fuel.
Russian planes aren't the most profitable, but I could have 4-5x more planes for the same initial investment. For bigger airlines like ALEX, investment cost isn't a huge problem so he can afford the optimal plane for an specific route, but I can't go expending 1bi in 767-300ER out of the gate, so cheaper russian planes offer a still very lucrative entry in intercontinental routes and heavy traffic.