In my experience, and opinion the Silver Stars are quick and easy, and look good. They give you a semi-hid look with a bit of extra light. The drawback is they are pricey for what you get. I've had 3 sets now, and all of them burned out in less than a year. The first set only lasted 3 months. I contacted Sylvania and they refused to do anything for me. Still they are a much better option than the cheap blue bulbs that claim to give you the xenon look. These things are dangerous, because actually put out about 1/4 the lumens of a stock bulb.
The 35 watt HID conversions put out less heat than a stock 55 watt bulb, and 3 times the light. That is if you choose 4300 to 6000k. 8k and higher starts to take a hit in lumen output. A decent HID conversion can be had for about the same price as SSUs, and will outlast them 50 to 1. I just purchased 3 sets of HIDs (35 watt low, high, and fog) for my new Bonneville @ $40 a set delivered on Ebay. They have the slim digital Xentec ballasts. I've been running a set in my 02 TA for quite a while now, and they seem very reliable, and exceptionally bright. If you like to go fast at night and see where you are going, go for the 4300 to 6k units. Mine are all 5k.