In addition to these giant items, there's also numerous compatibility fixes & other enhancements.
REAPER four.25 includes significant improvements including:
JS (user programmable audio/MIDI processing): much faster code generation for lower CPU use, new language features for code reusability, & outstanding bug fixes
Tempo envelopes/time signatures: overhauled tempo envelope & time signature editing for vastly improved behavior & usability
Theming: support for picture stacks for knobs & other additions to give themers additional control over appearance.
32 bit? 64 bit?
Most users will likely require to download a 32-bit version of REAPER. All versions of REAPER have a full-resolution 64-bit internal audio signal path from finish to finish, on all operating systems.
Your decision of which installer to download depends primarily on the plug-ins you require to make use of with REAPER & your operating method, & not on any audio quality considerations.