help need with wide angle or ultra wide angle lens
as mentioned in my introduction I am relatively new to DSLR photography but I am continuously improving.
I have used so far with my EOS 600D only a 18-270mm lens but now I have sees how nice it is to have a wide angle or ultra wide angle zoom lens for outdoor / fishing photography and therefore I am planning to buy one.
I am aware that my camera does not have a full frame sensor however I might anyway buy a full frame body after some time and therefore I definitely want a lens that is suitable for full frame.
I would like the lens to be as wide as possible however not so wide that I get a lot of distortion. Therefore my question what should I go for?
I know that for example a Canon EF 17-40mm F4.0L USM is considered very wide ..... however this is in combination with a full frame camera. With my current 600D it will be 27-64mm if I under stand it correctly (x1.6)?
Therefore I'm afraid it might not be wide enough for wide landscapes and outdoor shots I have in mind.
Should I therefore rather consider something like a Sigma 12-24mm F4.5-5.6 DG HSM II or will this give already a lot of distortion at 12mm? Since such a lens will be with my current body about 19-38mm I somehow think something like this would be better.
Of course it would also be interesting how the quality is between these two examples.
I am really grateful for any advice, help or suggestions.
Thanks and regards,