Cricut attempted last month to require a subscription service in order to use custom designs. While they did reverse the policy change after angering their customers it still seems like a big red flag on them. Apparently custom designs still require an internet connection and upload to their servers for some reason, if I understand correctly.
I'd certainly lean more towards Silhouette. I have a Silhouette Portrait 2 (smaller version of the Cameo) and before that had the original Portrait that was still going strong (unfortunately it was old enough that it wasn't compatible with Windows 10). Have made a ton of vinyl/mylar decals, paint masks, and printed decals on it. If all you are doing is making paint masks, the base software may be enough for your purposes as it can still import vector art in DXF format, which is exportable by most vector art programs like Illustrator and Inkscape -- or you could just draw your masks in the Silhouette software to begin with. Native SVG/PDF import functionality as well as additional features are unlocked with a $50 software upgrade and is mainly useful if you are doing complex print and cut decals (it's possible with the base software but it's a tedious dance and the upgrade is well worth it to avoid that). The software works without internet so there's no danger of shady stuff later on.