Project5 by Cakewalk is probably the easiest synth worsktation available. Easier than Fruity, even. It's what I do most of my work in. It's certainly limited in some respects, it's more loop and pattern based, for example there's no grand staff view for composing, it's just a sequencer. I'm personally looking to move on to Sonar, but it won't produce any audio (I fear it's my combination of Vista / Creative sound card). I'm looking into Sibelius as well for scoring. Problem being that Sib can't do VSTis so you're limited to certain sounds, and half the battle for me is the sound / instrument specifically, not the melodic line it's playing.
Really the bottom line is to play around, find things that you like. Everyone here has their own
preference of what they use. I've tried Ableton, Fruity, Reason, ACID for composing, and ultimately stuck with Project5 because it suited me best.