Good inverters:-
Power One - I have this myself
SMA - very German and ecellent service when needed
Not familiar with solarworld sunplug, sounds like a rebranded inverter, solarworld make panels, very good panels.
Stecca, 3.6TL - most efficient small inverter, should work with your 16 solarworlds - my favourite.
Fronius - Austrian, built like preverbal outhouse.
GoodWe - crap
Afore - never heard of, probably Chinese crap
Chinese stuff - only make I use is Samil for commercial installations. Chinese build quaility tends to be a bit iffy, they give long warranties as a selling point, but don't expect them to last 20+ years. SMA are designed for 25 years. Don't be fooled by A rating of inveters, you want AA or AAA - everything works at High Irradiance, but the quality stuff is good at medium and low irradiance which is where the extra As come from and boosts performanace on cloudy days and mid-winter.
How much are they charging you for the system? I can fit 4kW with Solarworld, SMA and German frame (Schletter) for less than £6k on a straight forward roof. Most companies offer good panels, but make a quick buck by using cheap inverters. The inverter is more important than the panels, it does the hard work, bit ideally you want good panels and inverter to make a good system. Try to avoid inverter in attic - they get too hot which eventually shortens its life and reduces efficiency in summer.
Incidentally, if your array isn't hghly visible ie front roof of house, don't bother with all black, they are more prone to overheating in summer and lose about 1-3% efficiency on the system. Do look nicer! The counter argument is that they warm up quicker in winter, but I've never been able to prove that argument either way.
just checked, the Sunplug is a re-branded Stecca