They both look like great chargers, there are pros and cons of both.
The GT1000 Duo wins on raw charge power though as it's capable of 2000W vs 1400W for the icharger. Obviously this is only an issue if you plan on using all that power and have a power supply man enough but it is a significant difference. Revolectrix's excellent reputation for reliability and (if you are in the right part of the world) their after sales service is good too.
The GT1000 being the 'simplified' version of the PL6 lacks a few of the more advanced customisation features that can be found in the iCharger but to be honest that's not an issue for 99% of users. The iCharger has a more advanced and data rich display, which is nice but maybe not a deal maker or breaker. One feature I regularly use on my iCharger that the Revolectrix chargers dont support is cross channel resistive discharge, that is I hook a high power resistor (a hairdryer in my case) to one channel and I can discharge several batteries in parallel at 1000W from the other channel. Maybe not everyone would find use of this but it's one feature that personally I'd struggle to be without.
It's a hard call between the two but i'm sure you wouldn't be disappointed either way so I dont really think you can go wrong. If you have access to local Revolectrx after sales service then that could be the clincher, and the battery discount is good too if you can source them.