Codec order for SIP - PSTN calls

[occamsrazor]

I'm looking for some advice as to what codec order I should set up in both my softphone and Voxalot. My setup is as follows:

X-Lite softphone <> Voxalot

Voxalot > Poivy provider for outgoing calls to PSTN numbers
Voxalot < Sipgate for incoming calls from UK PSTN number
Voxalot < SipBroker PSTN access numbers for incoming PSTN calls from other countries

Basically it is all SIP-to-PSTN or PSTN-to-SIP, no SIP to SIP calls.

SipGate say they support: G.729, G.711, iLBC, GSM, G726
Poivy say they support: G.711, G.726, G.729, G.723, GSMFR

My connection is Adsl 2mb down, 512kb up.

So my question is what codec order would you recommend for the softphone setup and/or each Voxalot provider setup, in order to achieve maximum call quality?

Thanks in advance,

Ben