FW can net you a pretty penny. A single small button can give you enough LP to buy a faction frigate BP. It costs you 2 mil, but you can then build the thing (for basically nothing) and sell it for 12-15 mil. If you're dedicatedly farming, I can see you earning 50-100 mil an hour. This is dependent on many things, though: Are there a lot of your side in the systems nabbing buttons? Are there a lot of enemies around trying to stop you? Even if you can't farm-claim a bunch of buttons, you can still easily make 50 mil an hour by simply sitting on small buttons in empty systems. Total time: 6-11 hours. Reliability: Mid to high.
L4 missions don't pay as well, but they're more predictable. If you use a well-fitted BS and speed run them, you can make probably 20 mil an hour or more - this includes the LP. You'll have to do some market research to figure out what's the best way to convert LP to isk, but you can easily see 1k ISK per LP. Total time: 25-30 hours of missioning. Reliability: High.
0.0 ratting is probably the least predictable, but I figured I'd throw it out there because you, technically, could make that work. The last officer spawn I got in 0.0 was Draclira. The fight took about 10 minutes, and netted me almost 2 billion in loot. Total time: Almost nothing. Reliability: Almost none.