Supernoodle - The powder coat finish will obviously still need cleaning, more to stop the build up of germs than anything, but it would be a heck of a lot easier to clean than plain aluminium which has a slightly abrasive finish. The other thing to bear in mind is the quality of the green powder coat. Greenhousesdirect say that they put on layer and layer, heat treated I believe, so that it actually becomes part of the aluminium itself, hence the price of a powder-coat finish. That said, do be really careful when it says powder coat, because some, no doubt, will be a simple paint on job, in which case I doubt it will last 5 minutes.
Makes - I paid for a guy who is sub-contracted to put up Rhino's and he said that there is barely any difference (certainly not enough to justify the price) between the harvester (which I have) and the premium. Both come with 4mm safety glass as standard, both have a 25 year frame guarantee (at least 10 more than I could find else where), vents are included, though louvres have to be added. The customer service was absolutely brilliant. The guy they recommend to put it up even came out just after the snow on valentines day! Elite, the GX range looked very, very good, but for the money and features the Rhino harvester definitely had the upper hand. Hercules also looked very good, but again, less years in guarantee and they actually ended up costing more. This is a major point by the way - do not be fooled into buying a cheap greenhouse unless it really is a budget thing, because they will end up costing a fortune. How anyone can sell a greenhouse without louvres and vents is beyond me, they are a must! And, do consider the base for the greenhouse, mine is drilled into patio paving, but the Rhino and some other makes, come with 2 different types of anchors, meaning you can erect on grass or concrete, saving a fortune in the grass case, as you don't have to pay for a concrete base to be built, they will simply need concrete poured around the anchors, much like a garden feature, arch, etc. so work out prices. Once you have done that, you'll find that the Elite and harvester are great options, if you have the money.
Do think of it as an investment. I absolute love mine and even in aluminium it looks the business. Everyone I know is really, really impressed by the build quality and general aesthetics. Actually, they're green with envy!