What is the difference, which one is better? I have tried to look into it, and it seems 12V strips are not brighter, but they need less current, and the voltage drop does not affect the colors that much.
Is this right? Which one is better for a regural desk-back moodlight (1,5 meters)?
With dumb RGB strips I would go with 12V, due to the lower current and higher efficiency, but with smart RGB strips (Individual addressable leds like WS1812) I would prefer 5V due to individual pixel control (In 12V strips they are usually grouped 3 pixels for each controller).
tosoki_tibor:
...it seems 12V strips are not brighter, but they need less current, and the voltage drop does not affect the colors that much.
Correct. Although the voltage drop/colours can be mitigated by using extra, good quality power wires to both ends & middle points to reduce the voltage drop in a 5V strip.
tosoki_tibor:
Is this right? Which one is better for a regural desk-back moodlight (1,5 meters)?
"regular"? For a moodlight, individual control of each led is probably not required, so the 12V type where only groups of 3 leds can be controlled, would be adequate.
You can even get 24V strips where voltage drop is even less of an issue than in 12V, and leds can only be controlled in groups of 6.
There is a trick here! 
There are two types of "12 V" LED strips or module chains.
If the strip has three LEDs - 6 wire chips - in series per WS2811 (black) chip, then all three are sharing the 60 mA current at 12 V.
If however there is only one LED per WS2811 chip, then this will still use up to 60 mA at 12 V, but the chip will be (getting warm and) wasting 2/3 of the voltage. These sorts of strips or strings are produced as a convenience of using a 12 V power supply, but are clearly grossly inefficient.
Here is a summary of addressable LED strips from The Hookup.
Voltage (Higher is better for less loss)
WS2811, 12-Volts, Least expensive. Disadvantage, Pixel grouping (one LED driver for three LEDs)
WS2812B, 5-Volts, Controller is in the LED package so individual LEDs can be controlled.
WS2813, 5-Volts, has a data backup line. (2-data in and 2-data out)
WS2815, 12-Volts, has a data backup line.
SK9822, 5-Volts, a bit more expensive, requires clock pin from GPU. (For signage with thousands of LEDs)
SK6812, 5-Volts, Has a separate White LED 4th Channel (0,0,0,255) AKA RGBW.
I am playing with the Alitov WS2811-5V LED strings.
I had a 5V led strip before, but recently I bought an RGB led strip that works on 12V. The power consumption is 7.2 W per meter. I bought it for my cabinet lighting and I think it works better than the previously led strip. I didn't have any problems and I'm really satisfied with the led strip that I decorated my cabinet. I bought the led strip on ukled.co.uk and I think you can find much more relevant information in a specialized online store market, you can even ask for expert advice and I'm sure they will provide with all the information you need.
GoodFollow:
You can find much more relevant information in a specialized store market, more than that you will have even a chance to check all the led lights
Absolutely rubbish.
Most people selling at these markets have not got a clue as to what they are selling, it could be coconuts for all they know.
CocUNOnuts!