Being that you are asking about a comparison involving an Altiris product and not solely Symantec products, My suggestion would be to go over to Experts Exchange or another vender neutral forum where different products from different vendors are recommended.
I personally have not used the Altiris product, although I understand your reasoning for comparing as Altiris has merged into Symantec now. I can tell you that from others in my field who have used the product that many were not satisfied and eventually switched over to BESR. My guess is that as they fold Altiris into Symantec, that particular product will be scrapped and current customers will either continue to receive support or will be offered special deals to move over to BESR.
Looking at the acquisition deal from my point of view, it looks to me that Altiris brings nothing new to Symantec's product line so I'm curious as to why they even purchased them in the first place. If anyone has insight on that, I'd be curious to hear it.