Personally, regardless of brand, I'd recommend staying away from all-in-one systems. Too many compromises are required, and repairs are considerably more tricky should they be needed.
Just think about it for a second. The computer is integrated into the monitor, so you can't very easily just go out and buy a new monitor to use with the computer if you want a bigger one. They typically use slower laptop parts to get the heat levels down, which also often means the few parts you can upgrade are going to be more expensive. Then, consider what happens if something were to go wrong with the system. Say the display goes bad. The entire system is useless until you get it repaired. Other computers you can just connect a new monitor to it and you're good to go. Repairs will also likely be more expensive if you don't go with the extended manufacturer's warranty (don't EVER buy a store warranty) which will add significant heft onto the initial sticker price.
All-in-one systems look nice, and when they work like they should, they can be. But as soon as something goes wrong, or you start to outgrow them, you're kind of stuck. A lot of people make the mistake of just walking into a store and buying a computer based on price. Then they wind up with some cheap POS Acer or HP system that has shoddy hardware (if we're to be extremely generous) and is a constant headache. The same sort of mistake is easy to make with all-in-ones.
Take a little while to just stop and think about what you're going to be using this system for, how long you plan to keep it, and what kind of a budget you have for it. Really think about some of the issues involving a computer besides how pretty it looks and how much it costs, which sadly is about as far as most people ever get. Try and decide whether you're absolutely sure that you're unlikely to need more RAM or hard drive space for the entire time you plan to own this system. If you have even the slightest of doubts, don't get an all-in-one. They can make for excellent guest room type computers. Something that won't be used too often, or for long stretches of time. They tend to fall flat for nearly everything else.