X2E-Z3C-W1-A - ConnectPort X2e gateway with standard ZigBee stack on it
X2E-Z1R-W1-A - ConnectPort X2e for Smart Energy Router gateway with ZigBee Smart Energy Profile 1.1 stack on it
The first Gateway is standard ZigBee, and the second is ZigBee with SEP 1.1 support, so the answer to your question is really going to depend on the Meter you wish to monitor.
My guess is that your Smart Meter is going to be a Smart Energy Coordinator, so the second Gateway is likely the one you'll want to purchase/use, and the first would be incompatible in its present state.
To address your other questions:
" I understand that these devices should connect to my Wifi (WPA2 security)"
Yes, the Gateways designated with the W1-A designation are Gateways designed for use in North America, which support Wi-Fi (WEP, WPA-PSK, and WPA-EAP are supported).
"Is the first product more flexible for my application?"
First product is likely Not Compatible with your application, due to my suspicion that your Smart Meter is going to be SEP 1.1, and the first Gateway is standard ZigBee (i.e. non SEP 1.1) only.
"It seems that both devices have the same Smart Energy Profile v1.1 so they should be compatible with my meter."
That is an incorrect understanding. Only our Gateways specified as SE (i.e. for Smart Energy) will work with other SEP 1.1 network devices. This is because Smart Energy Profile has additional requirements above and beyond standard ZigBee, namely in the area of additional security requirements such as Smart Energy Certificate management.
"How difficult it is to directly record the data (minute-by-minute electricity consumption at high resolution)?"
This is relatively easy when considering that the CP-X2e gateways in general (ZB and SE models alike) are tightly integrated for use with the Device Cloud by Etherios platform. All that would be necessary would be to create a reporting configuration on the Gateway, then access whatever data you're interested in from that Gateway (likely client cluster 0x702, attribs 0x0 and 0x400 on a CP-X2e SE Router gateway provisioned to a Smart Meter's network), via the Device Cloud. This configuration is quite common, and actively being used for this type of application by other customers currently.