The "best" really depends on many factors, as Rob's post notes.
Below are a few general ideas, without knowing more about your needs. I have excluded "budget" lines of speakers.
In the lower end of the spectrum, the new QSC K (2nd generation) series stuff is quite nice. There is lots of competition in this space, but I prefer the K's at that sort of price point, and QSC's powered stuff tends to be very reliable in my experience, and their new cardioid sub is good sounding and very compact.
2 tops and 2 subs will be in the $3500-6000 USD range depending on selections.
A slight step up would be something like the JBL SRX800 series.
2 tops and 2 subs will be in the $5000-10000 range depending on selections
If you want to get into very HQ pro powered cabs, take a look at Fulcrum Acoustic's FA Portable line, RCF TT series, L'Acoustics P series, etc. Expensive, but awesome, especially boxes like the Fulcrum FA22ac which are compact but incredibly powerful. The FA22ac is the nicest powered cab I've ever encountered at any price (albeit around $6000 each)
2 tops and 2 subs will be in the $15000-20000+ range depending on selections