A big part of the learning curve with microcontrollers is made up of the tool set. Arduino is much easier in that respect but you loose a lot of control and features in the IDE. For me this is a pretty big drawback, however if you have never done any micro stuff before Arduino is a good start to learn some basics and then move onto a more advanced chip/IDE like those from Atmel or Microchip. The IDE software is free so you could download it, take a test drive and maybe run through some tutorials to see which you like best.
I personally recommend the PIC Kit 3 package, which is affordable, comes with the programmer/debugger and sample test board. There is a bunch of learning material that compliments this kit. There are so many dev kits to choose from, researching and trying them is part of the fun!