Mike,
Looks like I'm a little late getting in on this thread. Sorry, been out on the road a lot lately fixing those blasted Automation Direct PLCs......... Just kidding.
Well, not in the last few weeks anyway.
I have lots of experience with Siemens S7-300, and AD 205 and 305. My personal preference is Siemens and here's why:
Hardware:
First, I should explain that my stuff goes on railroad equipment, and sees extremes in temperature, shock, and vibration. It's safe to say that they occasionally are operated outside of their manufacturers' environmental ratings.
AD - We have replaced lots of AD 205 cpus, i/o, and bases.
The AD 305 stuff has been better, but the vibration has its way with the snap-in modules.
Siemens - No failures yet. :nodi:
Software:
AD - I have never had training on the AD stuff, and it was easy enough to pick up and start programming ladder. I have only used AD on small, fairly simple machines.
Siemens- Can you buy a copy of Step 7, sit down, and start programming? It would be a challenge. But, a little training with a distributor can get you up and running in a couple of hours. I have had two Step 7 classes, and feel very comfortable with it. It's really no more difficult than the other guy's, it's just different.
Ladder, STL, FBD - pick whichever language best fits the task at hand - even within the same program. When it comes to math functions, STL is a gift from the gods. If you have done assembly programming, or have an HP calculator, STL is an absolute breeze. I tend to do my on/off logic with ladder, and arithmetic with STL.
If you need any remote I/O, profibus is fast, and it's a breeze to set up in Step 7. Just drag and drop. This was a major factor in my choosing Siemens.
Support:
AD - free phone support
Siemens - free phone support, plus a great local distributor (In my town, anyway)
In summary, at least talk to your Siemens distributor - and your AB distributor for that matter. This forum is a great place to get opinions, but I would caution you against making a purchasing decision based solely on what you read here (including this post). You are the one who is going to have to live with your decision.