Very much depends on what you want to do with the tank...do you want a softy tank, softy/lps tank or sps dominated tank? What is your budget, leds on a tank that size will cost a pretty penny, but would mean you'd probably never have to worry about upgrading again and you could keep just about any coral. Halides would be marginally cheaper but would cost more over the life of the lights (electricity, cooling demands, bulb replacement) . T5 is still a proven option, but at 24 inches deep you'd be looking into 6-8 bulb fixtures which can be both bulky and expensive to rebulb.
Also how do you like your tank yo look? Some people like a really blue tank...leds will give you a stunning blue look and give your coral plenty of pop. But both halide and t5s can be chosen in any number of combinations of color.
So give us an idea of what your dream tank would look like and I'm sure there'll be plenty of suggestions!
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