The Sig Romeos aren't great unless you get into the pricey ones. The cheaper options seem to have some quirks (mainly control related.)
The Holosuns are great, and have more features (shake awake for example) than the Vortexs.
I have two Vortexs, three different holosuns, and a Sig Romeo1Pro and they have all been great. If I had to choose - I like my Romeo1Pro cause it is larger than the others, has "shake awake" and a metal shroud, second would be holosuns due to the shake awakes, and third choice would be the vortexs.
Just be weary when ordering the mounts to make sure you get the mount that fits the optic you want to use.