Years ago, dive tables were the standard. These days, nearly all divers wear a dive computer and for good reason.
Your computer monitors depth, time, speed of ascent, and NDL in real-time. Tables give you a static plan. If you go shallower partway through, a computer adjusts. Tables are set before you get in.
Watch-style computers are the most common buy now. They're small enough, readable underwater, and you can use them as a regular watch too. Console-mount computers are available but fewer buyers choose them these days.
Budget computers go for around a few look at this hundred dollars and cover everything a recreational diver would need. You get depth tracking, dive time, no-deco limits, a logbook, and sometimes an entry-level freediving mode. The $500-800 range adds air integration, nicer readability, and extra nitrox compatibility.
Something new divers overlook is conservatism settings. Some algorithms are more conservative than others. A tighter setting gives you shorter no-deco time. Liberal ones extend bottom time but at a thinner safety margin. Neither is wrong. It comes down to what you're comfortable with and experience level.
Check with the staff at a dive shop who dives with various models before you decide. They'll give you honest opinions on which ones hold up versus what's hype. Decent dive shops have product guides and honest reviews on their sites as well