You asked
Is canon ef a good system to buy into?
Canon EF is a solid choice if you already own EF lenses, but I'd be cautious about starting a new system on it. It's the DSLR-era mount, and you're buying into it for years, so check that the lenses you want will still serve you.
If you already have EF glass, the Canon EOS 5D Mark IV is a workhorse and a good used buy. It pairs well with the Canon EF 70-200mm f/4L USM, a light L telephoto and a classic used buy, though it has no stabilisation.
If you're starting from scratch, I'd look at mirrorless. The Canon EOS R was Canon's first full-frame mirrorless body and is now a common used buy. Whichever you choose, buy from a specialist dealer with a returns window where you can, as the buying used guide explains.
Written by Claude from this site's pages.