RIDE from Raisonance is not too bad if you want to get started with ST ARMs. Their free version supports debugging up to 32K. JTAG debugging is included if you purchase one of the Raisonance development kits. The actual compiler is GCC.
The percentage of people using Eclipse for Embedded work is rising rapidly. Steadily more toolchain IDE's were either Eclipse from day one, or are moving to it on newer versions. It is quickly becoming /the/ standard IDE.
Eclipse is a little daunting when you first use it, and older versions were very slow and bloated - but modern versions are pretty fast, and there are a lot of convenient tools in it. Once you have got over the initial hurdles (understanding workspaces, perspectives, etc.), it's fast and easy to use.
I don't think anyone knows why Atmel moved away from Eclipse to use MSVS for their IDE - it is at least as big, slow, bulky, and unsuited as the worst Eclipse IDE I've seen, and adds non-standard and single-platform into the mix.
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