If you have good husbandry skills, a good size budget, a commendable devotion to the hobby, unwavering patience, and the ability to find someone to check the system twice a day in your absence, I'd say go for the reef.
But if you are the type of hobbyist who is devoted to your husbandry for the first few months, then slack off as the luster fades, then go with the Cichlids.
If you do want to go with a reef tank, you will want to either upgrade to a reef ready tank, or, providing the tank is not made of tempered glass, have the tank drilled and an overflow installed to make it reef ready. The benefit you have now with an existing tank is that you can have a "coast to coast" overflow installed.
There are several expenses involved with keeping a stable reef system. Suitable lighting fixture, skimmer, sump, return pump, power heads and live rock can all be considerable expenses. Depending on your source, you can expect to pay anywhere from $750 to $2000 on quality live rock alone. You may be able to cut that cost a bit by substituting some of that live rock with dead base rock, but for a system that size, you will want at least 100 lbs of Quality Live Rock (probably about 250lbs in rock total). As for the equipment, If you buy quality in the beginning, you alleviate the need to upgrade later.