I've been playing around hard with my home lab Asterisk build the past few months and have been testing various SIP trunk providers. My preferred provider is Flowroute with VoIP.ms coming in as a close second.
What I like about Flowroute is that they pass you the media stream from the media gateway that is terminating the call. So, in theory, you have the most direct audio path possible. In my testing, this seems to be true. When comparing latency with Flowroute vs VoIP.ms. In most cases Flowroute's latency is lower. In cases where it's not lower, it's unnoticeable equal to VoIP.ms (to my ear at any rate).
Pricing wise they are pretty similar. Flowroute is slightly cheaper outbound, but their inbound rate and monthly DID rates are higher (not by much, but depending on your usage could be exponential). Also, VoIP.ms has a lot more rate centers to choose from when buying DIDs via the web portal. Flowroute's can be limited depending on the NPA you desire, but I haven't reached out to their support (which is really good, as is VoIP.ms') to see if you can request rate centers in NPAs not listed on the portal.
I ported my home number to Flowroute and the process went without a hiccup. Was completed on the date and within the time window they provided.
A decent provider to play around with if you want something cheap and/or as backup is DID Logic. Their inbound/outbound rates are around $0.005/min and the cal quality/latency is good. However establishing an account is tough as they have this "anti fraud" process you have to hoop through.