If you are completing a small intricate steel structure, the best weld clamp magnet to use would be the adjustable links weld clamp magnet. This is because the adjustable links is the smallest weld clamp magnet available, so is the best for fitting into the smallest gaps.
The best weld clamp magnet for extensive use of irregular angles, for example 127°, would be the variable angle weld clamp magnet as it can moved easily and set to any angle.
If you are using a weld clamp magnet for creating standard steel shapes (box section steel) then the best weld clamp magnet to have would be a fixed multi angle. This is because it has angles pre-set into their shape so are quick and easy to use.