Tables used to be the standard. These days, nearly all recreational divers use a dive computer and it makes sense.
The computer calculates depth, bottom time, ascent rate, and no-deco limits in the moment. Tables give you a static plan. If you move between depths during a dive, the computer recalculates. Tables are set before you get in.
Wrist-mount computers are the most common go for at this point. These are compact, readable underwater, and you can use them as a watch between dives. Console models are available but less divers go that way now.
Entry-level computers go for around $250-400 and handle everything most divers requires. You get depth tracking, find here time, NDL, log function, and usually an entry-level apnea mode. The $500-800 range includes wireless air monitoring, improved screens, and additional mix compatibility.
What buyers overlook is how the computer handles. Some algorithms are tighter than others. A conservative computer results in reduced NDL. Looser settings extend time but with less safety margin. Neither is wrong. It just your style and your diving background.
Worth talking to someone at a dive shop who's used various computers first. Staff will have real-world feedback on what's good and what's marketing. The better Cairns dive stores have gear reviews and honest reviews on their sites too