if you are only wanting to apply a modest amount of limiting, I like this one: Missing features - Audacity Support
For more aggressive limiting, I’d go for: Peak Limiter
(I’ve been considering changing the name of “brickwall.ny” because there is some confusion between this and a “clipping” effect. “brickwall.ny” is a “limiter” not a “clipping” effect.
If you mean the LADSPA effect, then yes it is a clipping effect, but also provides a degree of “reconstruction” (adding back a scaled version of the peaks) so as to moderate the hardness. There are also a couple of “soft clipping” effects here:
Generally I would apply compression first, particularly when using a compressor that does not use lookahead (such as SC4).
If the uncompressed audio has occasional high transients, then you may want to use a limiter to moderate those first (more likely with music than voice recording).
For performing “loudness maximizing” it can be useful to apply limiting both before and after. The first pass to handle transients, and the second pass to squeeze out just a bit more loudness after using a lookahead compressor.