Years ago, dive tables were the only option. Now, the majority of divers use a personal dive computer and for good reason.
Your computer tracks your depth, bottom time, speed of ascent, and NDL in real-time. Dive tables are a fixed calculation. If you change depth mid-dive, the computer recalculates. A table can't.
Wrist-mount computers are what most people buy these days. These are compact, readable underwater, and you can wear them as a regular watch as well. Console models are an option but less divers go that way now.
Entry-level computers run about $300-odd and cover everything the average diver would need. You get depth tracking, time, NDL, a logbook, and often an entry-level freedive function. The $500-800 range includes wireless air monitoring, additional information improved screens, and extra nitrox modes.
The one thing buyers don't think about is algorithm differences. Some algorithms are more cautious than others. A conservative algorithm gives you reduced NDL. Looser settings allow longer time but with less buffer. Neither is wrong. It comes down to your style and how experienced you are.
Talk to the staff at a dive shop who uses various models before buying. Good dive stores will have real-world feedback on which ones hold up versus what's marketing. The better Cairns dive stores have product guides and rundowns on their websites too