What I'd rate them on / what I'd like to see
1. No unreasonable underhand charges (35p per minute or part thereof for Answerphone-access [Orange] - 10-12p/min is tolerable, but should really come out of inclusive minutes on predominantly voice-contract; £15 step-charge for going a few MB over a multi-GB monthly data allowance on a data-contract [Vodafone])
2. Option to have text notification of imminent exceeding of data-bundles sent to a phone/device other than the device at the centre of the contract (e.g. to a phone handset rather than the data-dongle)
3. 24hr support for network-related issues
4. Acknowledgement that network faults can and do occur. Three and Orange have no specfic means to report faults or suspected faults, and they do not acknowledge such issues (masts down etc) on their websites.
5. Transparency about what's permitted or incurs additional charges on data packages (e.g. Skype)
6. For data connections, not just raw throughput, but ping-times [Three consistently quicker than Voda in my experience] and propensity to mangle (proxy) data connections [in my experience Voda causes spurious delays and random http 504 errors (4+ years now) and web pages which just intermittently never get returned (including some banking sites)].
7. A commitment from telecos to resolve longstanding issues (see 6) rather than constantly deny them or fob folks off with try updating this, that, or the other, try in a different location, try standing on your head etc etc.
8. Admission from the phone co when there's some fundamental problem, e.g. which is stalling data to dial-up modem speeds (40kbps) for much of the evening for months on end, despite excellent signal strength [Orange].
9. Greater flexibility with contracts - e.g. more shorter-term/flexible options rather than 2-year contracts (which have to be paid in full if you quit early) even when there's no appreciable device-subsidy.