Using the SCART is better from the Toro, here’s why:-
1 – Dreamcast games running in 240p and 480i will benefit from the low-pass filter available on the AV1 input but not available on AV3. 480p games will not be affected either way.
2 – AV1 is set to automatically default to 480p rather than 640×480. 480p is the correct setting for Dreamcast (though you should also change the advanced timings as per the wiki for best results).
3 – Interlace running on AV3 works, but it’s kind of a hack and it can cause problems, no such problems on AV1.
4 – The timings for H&V sync seem a little strict on AV3 and some users have complained this causes image drop outs (this is a theory as I’ve not been able to replicate it personally).
Now if only the Toro didn’t have that annoying detachable cable that likes to keep coming loose 🙁