This topic has been discussed a lot on the past... but I'll summarize, since thats all I know I wanted when I went looking back a few months.
1. The 70-200 will work with the 1.4x and 2x conveters, WITH autofocus still functional.
2. The 70-200 alone is sharper than the 100-400 up to 200mm. AF
3. The 70-200 + 1.4x is slightly sharper than the 100-400 up to 280mm. AF
is about equal. 98-280mm F4.
4. The 70-200 + 2x is not quite as sharp as the 1-4 up to 400mm, but its close. AF
is slower, but more accurate. 140-200mm F5.6
5. The IS
on the 70-200 is 3rd generation, and is more highly regarded than the Gen 2 on the 1-4.
6. 70-200 and converters will run you a bit more than the 1-4.
7. 1-4 is lighter, with a larger "zoom" amount (4x compared to 2.9).
8. You can't beat F2
Having used a 1-4 and 70-200 with 2x, I'm going to go with the latter. It's still plenty sharp, the AF
is still plenty fast... I prefer the ability to have F2
.8 when I need it, and back out to 70mm when I know the stuff is going to be close.