Both the SP1000 and the Lotoo PAW 6000 are great DAPs, I have both of them and I will tell you it's mainly a preference of sound signature that will make you decide.
The Ultima series from Astell&Kern all have pretty the same sound signature, a very balanced tuning that sounds a bit warm. The SP1000 specifically, has a pretty wide sound stage and decent imaging. Maybe a bit forgiving on poorer recordings. Very great DAP that you know can really "amplify" the music in your files almost everytime.
The Lotoo on the other hand like its bigger brother the PAW Gold Touch, has a cold analytical sound signature, it is truly a reference style DAP and the sound is closer to your ears compared to the SP1000. The DAP sounds very detailed but I would becareful about which IEMs to use with them because in your face very resolving IEMs like the Campfire Solaris in combination with the Lotoo P6K can sound harsh at times, almost as if there is way too much detail going into your ear canal.
I really love the Lotoo's sound signature because it has a very strong studio imaging in the sound and can make recordings in your music files sound as if they were playing it live as you listen. A very cool effect!
Not to mention the player has a custom OS that is lag free and the 5 second boot time and power off time.
I love both DAPs for their own reasons and if you were to choose either one just go with what sound signature you prefer.