Some thoughts about Resize filters:
Lanczos Resize filter in Hybrid is slightly sharper than Resolve "Sharp" resize filter in project settings. But difference is very small and overall they produce 99% the same result.
Resolve SuperScale filter in Clip Attributes is with Sharpen/Noise Reduction set to Low/Low is definitely sharper than Lanczos Resize filter in Hybrid. For my subjective opinion it look too sharp and too plastic for SD sources upscaling.
Lanczos + NNEDI3 neural network resizer seems the best. It removes jaggies upscale artifacts on contrast diagonal lines, but doesn't add artificial oversharpening. On maximum settings it is very slow.
Here are SD to 1440x1080 renders additionally 200% magnified to see the difference:
It appears that if you use NNEDI3 Resize, it always use only its internal resize method (looks like based on Lanczos) and don't depends of Resize method selected in "Crop/Resize" tab at all.
In case if for some reason you decide don't use NNEDI3 Resize, here are some test results of different Resize methods in "Crop/Resize" tab:
8 - Sinc: adds very aggressive sharpening effect
9 - Lanczos: tiny sharpening, crisp looking, OK for everyday.
3 - Experimental: sharpness somewhere between Bicubicspline and Lanczos.
10 - Bicubicspline: slightly softer than Lanczos
2 - Bicubic: softer than Bicubicspline
7 - Gauss: softer than Bicubic
Here is another interesting test. Poor quality chroma edges from miniDV camera where magically fixed by NNEDI3 resize. Further NNEDI3 Upscale to QHD (1920x1440) and UHD4K (2880x2160) compare to HD makes no real difference in quality even if compare side by side on UHD4K timeline.
Some people recommend 960x720 as a master copy for deinterlaced video because 1280x720 @50fps allows to playback from bluray disc, but as you can see NNEDI3 resize to 960x720 looks softer than NNEDI3 resize to HD. So i personally recommend 1440x1080.
Another interesting option is 1556x1152 (this is dual 768x576). It allow to crop black borders and fit source to 1440x1080 in Resolve without additional upscaling step.
Tests made on UHD 4K timeline:
QTGMC SLOW-FTS0,
NO RESIZE
QTGMC SLOW-FTS0,
RESIZE to 720p NNEDI3-32-N2-P2
QTGMC SLOW-FTS0,
RESIZE to 1080p NNEDI3-32-N2-P2
QTGMC SLOW-FTS0,
RESIZE to 1440p NNEDI3-32-N2-P2
QTGMC SLOW-FTS0,
RESIZE to 2160p NNEDI3-32-N2-P2
