Software does not wear out, but font tooling does go stale — file formats get abandoned, single-vendor apps get discontinued, and web services vanish taking your workflow with them. If you are choosing what to build a type pipeline on, longevity is the real criterion. Here is how the options score on it.
Four questions, applied to any tool in this space: Is the source format open and documented? Can the tool be scripted without a GUI? Is there more than one maintainer or vendor? And if it disappeared tomorrow, could you get your work out? Everything below is graded against those.
The Python fonttools package is actively maintained, used inside the pipelines of major type foundries and font hosting services, open source, and fully scriptable. It reads and writes every format that matters and can dump any font to XML with ttx, which means nothing you produce with it is ever locked in. If you are choosing one thing to depend on for the next decade, this is it.
The single biggest durability decision is not which editor you use but which format you save in. UFO is an open, documented, directory-based source format that every serious editor can read and write. Proprietary formats are convenient right up until the app is discontinued or its licence server changes — and that has happened repeatedly in type design. Keep UFO as the archival source and treat any editor's native format as a working file.
Browser-based converters and subsetters are convenient and have the worst track record for still existing in five years. Several widely-used generators are now years without an update, still producing formats — EOT, SVG fonts, the full four-format @font-face stack — that no current browser needs. If a step in your build is a web form, replace it with a command: pyftsubset for subsetting, woff2_compress for conversion. Both run offline and both will still run next year.
Icon fonts, superseded by SVG. The bulletproof @font-face stack with four formats — woff2 alone covers every browser you support. EOT, TTF and SVG font fallbacks. And font CDNs as a performance strategy, since browsers partition their HTTP cache per site and the shared-cache benefit no longer exists.
Source in UFO, in version control. Build with a Python script calling fontTools. Subset with pyftsubset --flavor=woff2. Self-host the output. Every step is a text file or a command, nothing depends on a vendor staying in business, and the whole thing can be re-run from a clean machine with one pip install.