Your Herakles can make lots of flavor, but needs more power to do so. I find it just begins to get interesting in the 56-57w range. Other than being smaller, not sure if the Hydra is any different from the standard Herk that I am familiar with. Ni and Ti are becoming popular because of their Temp Control capabilities. Another option is the Crown, using the stainless steel coils. Very nice tank as long as you have the patience to do a lot more coil priming than with your other tanks.
You might start with the mod rather than the tank when considering the tanks you are referring to. A basic Eleaf iStick 100w without TC can easily be found online for around $40 from the US..... or less from China, but not sure I'd risk it over $8 or so. Not saying it's the best mod, but it would get more flavor out of the Herk, Crown, Arctic, TFV4, etc.
Your eLeaf 30 could certainly power a Kanger Subtank Mini with the 0.5 ohm vertical coil. Nice flavor and good daily driver, but flavor and clouds not really up there with the big boys...... not its' purpose in life. I use it as a daily driver, or for when I want 6 nic rather than 3 (the higher nic more tolerable with the lower powers).
