I am very interested in onomastics
So, let's say that in modern Bulgaria there are two trends of naming babies.
One is with Western names, the other is with old names of the rulers.
In the Rulers' trend, more common are the tsars' names, such as Samuil, Simeon, Ivan-Asen, Kaloyan, Boris.
The khans' names are rarely given, the most popular are Krum, Kubrat , Kardam
(which I personally adore, but I guess we'll have to choose Simeon), Asparuh (rare), Tervel, Presian...I have heard of one Sevar.
Omurtag is rare now, Toktu - not given, Bayan - never heard of someone called that.
I've read that Boyan is the slavic form of Bayan (which is mongolian).