LOST,
IMO, in pure picture terms (I only tested both with 2D blu-ray), it is identical. The picture processing technology (P4HD) is afterall the same in both machines. Not sure about 3D material.
The BDT-310 is better sounding though, with a greater depth and richness not found in the BDT-110, which sounds leaner. It also possesses a very smooth tube like sound quality (no doubt due to the DTS feature) that sounds great even with regular CD's.
The BDT-310 also has some additional features like the Dual HDMI's, Touch Free Sensor that opens and closes the disc tray (does not always work, though!), built-in Wi-Fi and Digital Tube Sound (besides the standard High Clarity Sound, which was always great!).
The Dual HDMI's would enable you to use the 'main' output to transmit 3D pictures directly to your TV while the second 'sub' output can be used to send HD audio to your receiver, which is great if your receiver lacks v1.4 inputs.
The Pioneer BDP-LX52 is still a good blu-ray player (picture and sound quality only) in isolation, although I still find that it performs best when partnered with a Pioneer TV rather than any other TV.
Ronald