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MM-1 is really easy to use and hard to make it sound bad. Not a lot of tweakability but it gets the job done. Transparent and Wide mode are both great. On sale at the moment for $89 and it's included in Softube Volume 5.
MD4 has an amazing ability to pull details out of a mix (try the DXP presets!) in the same way as Zynaptiq Intensity but without the harshness that Intensity adds. TONS of functionality built into a friendly UI. The full System 6000 pack is well worth the investment.
Unisum is very tweakable, to the point of being intimidating in advanced mode, but there are lots of excellent presets to help you learn how to use it fully.
Sonnox Inflator is another one worth checking out - at $39 it's a bargain. Old but still very good.
The good news is, all the above are available for full free trials - I'd encourage you to try them all and see which you're most comfortable with. Personally I love MD4 - it's a miracle worker on old material!