The 77-830 is my pick, only because love the old Cybernet circuit boards. The 510XL does have better transmit audio, because they use a different type of mic (Electret condenser) that has a wider audio range. The more common dynamic mics used on many other radios will not work. I do a number of mods on the 77-830. To name just one, I always change the mic jack wires inside to except all 4 pin Cobra dynamic mics. That allows me to experiment with many other mics, including power mics to suit my vocal taste. On the downside, the 77-830 is old and fat. Perfect for mounting under the dash in older cars and trucks, but too bulky for many other vehicles. It will also need some of the capacitors changed either now or in the near future. Make sure that mounting brackets and screws are included on whatever radio you choose. Unless you make your own, they're pricey nowadays. Look closely on the back of the radio for signs of rust or corrosion. If the cabinet screws look burred like someone used an improper sized tool, buyer beware....novice fingers have probably been messing around inside.