This is just opinion from experience so take it for what it's worth. ATS34 and 154CM are pretty much the same alloy, but have very different challenges. ATS34 got a bad rap some years back for, among other things, internal flaws. These only showed up in about 1 or 2% of blades, but were a pain because much of the grinding was done by the time you found it. As noted above, we haven't seen much of the clouding issue lately, but the internal flaws still show up from time to time.
154CM has it's challenges on the outside (like most of crucibles steels). To remove mill scale, they sandblast it and this leaves a sort of pebbled finish that some makers go crazy trying to remove. This can be eliminated completely by surface grinding or by ordering ground barstock. It also comes off pretty easily by running the bar lengthwise against a contact wheel with a 60g belt. Internally, 154CM is nice!
Both of these are good blade steels producing quality knives at reasonable price.
I tend to get howls of outrage when I offer my opinion on 440C, so I'll just quote what crucible has to say on their 154CM spec sheet. Howl at them if you like. :3:
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"154 CM has better corrosion
resistance, better wear resistance and better
hot-hardness than 440C. For knifemakers, it
offers better edge retention than 440C. It also
has higher attainable hardness and better
through hardening characteristics than 440C."
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Since you posted this under heat treating, both ATS34 and 154CM heat treat the same with very close - and repeatable - results.
Rob!