Both are loss less compressed.
"Exclusive to Nikon cameras, the NEF is Nikon's RAW file format. RAW image files, sometimes referred to as digital negatives, contain all the image information captured by the camera's sensor, along with the image's metadata (the camera's identification and its settings, the lens used and other information). The NEF file is written to the memory card in either an uncompressed or "lossless" compressed form. "
Raw Photo Format for SLR Cameras | Nikon Electronic Format (NEF) from Nikon
NOTE :
1. In older cameras there was an option for having either lossy or lossless compression. With SD card storage costs plummeting and sizes increasing, there is no longer any rationale for lossy compression.
2. Though both D5300 and D3300 have the same sensor, the D3300 RAW file is available only in 12 bits. This in my opinion is just to justify the higher cost of the 5xxx series.