Depends very much what interests you... In general, you can't go wrong, or much wrong with kits manufactured by Tamiya, Hasegawa, Fujimi. However, even those excellent manufacturers have the odd bad kit, and some of their older offerings are not up to today's standards in detailling and engraving.. Revell-Germany's kits are often very good too, but again, their earlier offerings should be left on the model shop shelves! Italeri is a decent company too. Ans so is Academy/Minicraft. Revell, Italeri and Academy have more esoteric subjects than the three big Japanese companies... However, they re-market Matchbox , Zvezda and Hobbycraft kits that are not always of the best quality... If you are into even more esoteric subjects, it is time to consider Eduard, Roden, Trumpeter, BlueMax, KP, or why not, 'garage' companies such as Welsh Models, Aeroclub.
Tell us what you like and I'm sure there are people here who will be able to direct you to the best kits out there!