I wouldn’t recommend sharpening images in AE unless you have no other choice. AE will accept almost any image file format so its best to use an uncompressed (or low compression) format like EPS, AI, PSD, TIF, etc., although high-resolution JPGs are usually fine too. Personally, I like using PSDs and AIs since they’re Adobe formats so AE supports more functionality with them. For example, you can set up an entire AE project in PS using layers and layer sets, which will become Comps with layers in place, if imported into AE as “Comps” or “Projects” (I just don’t recall the term AE uses). Regardless of most file formats, you’ll lose quality if you scale the image beyond 100% in AE. AI, EPS, PDF (and probably others) are exceptions to that, if you use “continuos rasterization”, but the trae off is that limits how you can apply FX to those layers (you’ll have to precompose or use adjustmnet layers).