Basically I don't give a thing whether it's metal or resin. As long as the casts are good and the models are interesting I'm a happy customer. Sometimes I do like resin more than metal as the castings are better most of the times. In addition, they don't chip as easily, making them really nice for gaming too. On the other hand, if the castings will be like Ilyad Games' resin casts, then I'd say you REALLY need to go for metal (the casts had loads of flash and the occasional huge air bubble that had evaporated the resin...fantastic sculpts but horrible casts).
The size doesn't matter at all to me. I never understand the fuzz about 28mm vs 32 mm. On the gaming table you don't see the difference (especially if you are creative with basing) and both scales look cool. As a painter I prefer 32mm as it usually has a bit more detail than 28mm and allows for more freedom in freehands, blends, etc.