Do you have a budget? Mac or PC? Defining both will help narrow down the options. Do you need to do any editing, or simply sample rate conversion (SRC) and dither?
For a mostly freebie option, use Audacity (free) for editing, if any (exporting to 32bfp and same sample rate as the master recording), R8Brain Free for SRC and dither, and CD-Wave ($15) for tracking.
IMO, the best low-cost option - and having the best workflow and great quality processing, SRC, and dither - is Samplitude SE @ $50. For example, in ABX testing, I couldn't hear a difference between SAM SE's SRC at it's highest quality setting and the very well regarded R8Brain Pro or Free. But that perhaps reveals the limitations of my playback / ears, and not so much the SRC used by each app. Note, however, that SAM SE has a steeper learning curve than most of the other apps.
For $$$, lots of options including Steinberg WaveLab, Adobe Audition, Sony Sound Forge, a handful of Mac apps, and I'm sure some other options about which I'm forgetting.
Lots of personal preference involved. My favorite dither so far is MBIT+, which is built into the iZotope Ozone plugin (and perhaps a Mac editing tool or two). But it costs a couple hundred bucks. To keep my workflow simple and costs down (and sacrificing very little quality, if any), I stick with SAM SE for dithering. Others prefer UV22HR dither available in WaveLab ($$$). Still others prefer Sound Forge, at least a few Mac apps, and I'm sure some others I'm forgetting, as well.
Defining OS, budget, and your editing requirements will help narrow down the choices.