Years ago, dive tables were the standard. Today, the majority of divers use a dive computer and it makes sense.
A dive computer tracks your depth, bottom time, ascent rate, and no-deco limits in the moment. Tables give you a static plan. When you move between depths partway through, the computer recalculates. Tables don't.
Wrist-mount computers are what most people go for at this point. They're compact, readable underwater, and you can wear them as a watch between dives. Console computers are an option but less people pick them these days.
Budget computers run about $250-400 and cover everything a recreational diver requires. Features include depth, bottom time, no-deco limits, dive logging, and usually a basic freediving mode. Stepping up to mid-range adds transmitter compatibility, better displays, and extra gas compatibility.
The one thing buyers forget is algorithm differences. Certain computers are more conservative than others. A tighter computer gives you reduced bottom time. More aggressive settings extend bottom time but at a thinner margin. Both work. It's personal preference and how experienced you are.
Check with people at a Cairns dive shop who's used multiple computers before you decide. They'll offer honest opinions on what's good and what isn't hype. The cairns dive computers better Cairns dive stores put out buying guides and comparisons on their sites too