It all depends on what you're looking for and how much you're willing to spend:
For something cheap and accessible, with the biggest range, the Bandai Movie Monster Series is where it's at. The plastic is softer and is generally more geared towards kids, but some of the sculpts are actually surprisingly decent.
The next step up would be NECA's offerings which have better articulation and sculpts while maintaining an affordable price point for casual collectors. For many this is the sweet spot but they have a limited selection of characters - mostly just Godzilla.
After that comes SH Monsterarts, which offers premium articulation and very good sculpt work but often at the expense of screen accuracy and paint apps. The line is also notorious for its unpredictable QC and ridiculous aftermarket prices.
Finally, we have the X-Plus line of statues. These don't have articulation but are considered the best of the best when it comes to sculpt and paint apps. Just be prepared to pay a hefty premium but they are worth it for the right design.
That about covers the major lines. There are other companies that make trading figures which can range from garbage to pretty good but they're not the most consistent so I don't include them.