Wow what a question, I have the 100-400L the 70-200L and they are great lenses but quite heavy.
You really need to decide what you want to cover, Macro, birds wildlife portraite landcape or just one lenses that does a bit of everything, and when you decide save for the best lense, as any make do lense will always make you feel you could have got a better shot.
So some soul searching about what tickles your fancey then come back and ask which lense you should get because there is such a wide choice with lenses and price.
Hope this helps
Ps I read a quote but it was too late, it said: If I knew how much photography was going to cost me In would never have started