Back in the day, tables were the standard. further reading At this point, nearly all recreational divers wear a wrist-mount computer and it makes sense.
The computer calculates depth, time, ascent rate, and no-deco limits in real time. Tables give you a static plan. When you move between depths during a dive, the computer recalculates. Tables don't.
Wrist-mount computers are what the majority of divers use now. These are small enough, readable underwater, and you can use them as a watch between dives. Console computers are still around but less divers go that way these days.
Entry-level computers start around $250-400 and handle everything the average diver would need. Features include depth, time, no-deco limits, log function, and often a basic apnea mode. Stepping up to mid-range gets you wireless air monitoring, improved readability, and additional mix compatibility.
What buyers forget is how the computer handles. Certain algorithms are tighter than others. A cautious setting gives you less bottom time. More aggressive settings allow longer time but at a thinner buffer. Neither is wrong. It's your style and experience level.
Check with the staff at a dive shop who's used multiple computers first. Good dive stores will give you honest opinions on what works and what isn't marketing. The better Cairns dive stores publish buying guides and comparisons on their websites as well