1.4 Multiplyer for Canon/Sigma
 

I have a Canon 30D with Canon 75-300 and Sigma 170-500 lenses.
Any suggestions as to best compatible multipier.

I've tested a 1.4x tc (actually tried both Kenko and Sigma) on the 170-500 with a 350D - neither gave AF and there was an obvious drop in IQ. Personally I wouldn't recommend using a tc with this lens.

They wouldn't give AF - the Canon is f5.6 at the long end and the Sigma f6.3 IIRC. Add a stop for a 1.4x TC and you're outside the AF spec of the camera.

I don't know which make/model TC would give the best IQ, but I can tell you that the Canon one won't fit.

Remember that you can not use the Canon's original 2x TC with either lens as it won't physically fit. I don't know for sure about 1.4x though.
As for AF, as long as your final F stop is less than 5.6, you should be able to have the benefit of AF, but even at best with canon's Mark II 2x tele-extender, I see a significant drop in AF performance even with 70-200mm L 2.8 IS.
General rule of thumb; Reserve TC only for few occasions. If you need the final focal length for routine use, consider buying that focal length in first place.

I use my 20D with a sigma 170-500 and 70-300 DO IS both with a Kenko 1.4 Pro and get autofocus with both though it can be a little hesitant with them unless there is good light/contrast. With some camera bodies like the 20D and probably the 30D this seems to work. Quality is still very good with the 70-300 but a definate drop with the Sigma. I reckon its better to leave the converter off with this lens and crop on the computer. The Canon converters will only fit with specific Canon lenses so you would have to check which ones, I don't think they would work with either of your lenses as the glass elements of the converter and lens will hit each other due to the design.