Just installed a larger PBX (well large for us, about 50 extensions) and the customer went with AT&T SIP over fiber shared with their main internet connection (aka AT&T Flex BVoIP). At our office we have SIP over a dedicated T1 from Windstream. Both have proven to be reliable. We did have a 5 minute or so Windstream outage this past fall, however.

We have a third customer that has a PRI over fiber from AT&T.

In every case, however, the SIP was provided by the company providing the circuit. I've tried third party SIP providers at home (using pro grade equipment) and it has not been as reliable.

As long as your PBX plays nice with SIP, the SIP trunks and circuit are from the same provider, and the circuit is of good quality, it seems like a safe choice.