they will both provide you with sufficient margin of safety as you aren't doing decompression. Neither is better, they're just different. Most prefer Z+ as DSAT is pretty outdated in my opinion, based on the PADI tables which are the most liberal of the standard dive tables for repetitive diving.
Neither is more or less conservative across the board, the difference is in where the conservatism is rooted.
Z+ is more liberal on single deep dives, but more conservative on shallow ones, the DSAT is more conservative on the deeper stuff but generally more liberal on repetitive dives. So if you're doing standard recreational profiles, multiple dives a day all shallow etc, Z+ is probably more conservative, but if you are doing one or two deep dives per day, the DSAT is more conservative. Take surface intervals into account and the Z+ works better with long surface intervals, DSAT works better for divers wanting to maximize bottom time on quick turnarounds. Make sense?
For me if I had to choose, I'd use Z+ for most of my diving, which is one longish deepish dive in the morning, have a 2-3 hour SIT, then one in the afternoon. Deepish/longish is about 90minutes at 100ft. This would give me shorter decompression obligations than DSAT.
For reef type diving, quarry diving, etc where it is up and down up and down, short 30-40 minute dives at 30-50ft with 1 hour intervals, then DSAT would give me more bottom time and less deco than Z+. If you were trained with PADI tables and are using them to check the computer, then use DSAT as it will best replicate the tables.
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