I'd always prefer plastic, but I think something you need to consider before saying everything needs to be plastic is the time and cost aspect.
To make a mould takes a lot of time, which I think is one of the main reason there has been a bit of bottleneck in Rubicon's releases. A mould also costs a lot, you have to sell a lot of kits to make the money back and have the initial capital to produce them. Warlord's advantage is that they are the game and new players will see their kits. Rubicon on the other hand (despite being better for the vast majority of kits) are discovered either via word of mouth, advertising or at stores.
Metal and resin kits in the other hand, the moulds are relatively cheap and easy to replace. They're great for items you know aren't going to sell in huge amounts (which is a great sign for lesser know and rarer tanks done by Rubicon is resin). its why warlord's infantry are (for the most part) plastic, but all the teams are metal.
Rubicon have not confirmed if the infantry will be plastic or metal, but they have hinted something to do with metal in a previous post. They also showed their design for bases, which have dimples on to assist with gluing (why would you need these for plastic?).
You could put good money on some tank crews and infantry being metal and not plastic. For a company with experience in making plastic tanks, an initial plunge into infantry in metal would probably be better for them. Making plastic infantry is a whole different ball game than tanks.
Does metal put me off? A bit. I'm not a fan of painting metals, but if I could get US infantry in a Perry Miniatures scale I would use them. No more melon heads and gorilla arms!
But as ripley said, metal vs plastic vs resin... it'll always be debated and no one will be right or wrong whatever you think. It's just your preference.
