The oil based would stay in your system longer when injecting, but I dont know about effectiveness difference. And yes, you can drink oil based winny too. Injecting is much better though.
about the only difference i can think of is that the oil based winny will be slightly less painful when injected. the water based product when injected will have the water absorbed by the body very rapidly thus leaving the winny crystals siting on the muscle itself causing irritation. the oil will take longer to absorb so the crystals will not be immediately exposed to the muscle tissue and it will not hurt as bad when injecting. it will still hurt some though but the oil based will also be easier to mix with other oil based products and injected together.
any product that can be injected versus orally taken will be better due to the fact that a much higher concentration of the product will be able to enter your bloodstream to be used. the digestive system can be very destructive and break down and damage a good portion of orally taken products thus decreasing the efficiency.