Pros: Amazing W/C potential (240mm native at the top, 240mm at the front,120 at the rear), Build quality, innovative layouts, removeable HDD cage, quiet
Cons: Hard to remove the side panels, not exactly dust filtered, instead its more like a sponge (keeps out noise I guess)
Aesthetics: The Fractal Arc is obviously different from the Define. The Define takes a more literal approach to sleekness and places a gloss door onto the front. This makes a very eye-catching on any table, and is really nice to look at. The Arc is sleek yes, but differently. It uses a more subtle design, using a large mesh front and round edges, being understated, appealing, yet telling the world "This case is owned by a guy who doesn't like childish designs". It looks good But, appearance isnt where the Arc shines in.
Building in it:
It is very spacious tbh. Removing the upper HDD cage allows me to move my arm abit more inside and the width of the case allows more freedom as well. BUT, there are a few niggles. For my case (yours might differ), the side panel (with the fan) is extremely tight. Secure it definitely it, even without the thumbscrews holding it in, I dont see how the panel can fall off by itself. So, tough that it is requires a very strong tug to pull out. Next is the PCI slot covers+screws, I installed my mobo fine (missing 1 mobo standoff under it but it is fine), and then my GPU. The GPU is somehow not very well aligned to the screw holes in the Arc. I tried to use the thumbscrews that was orginially there to screw it in, while pushing the GPU towards the end, but it will just not go in. After 15 mins, I had to use another screw (non-thumbscrew) to get the GPU secured. I believe this problem is exclusive to my unit as none of the reviewers or other users reported this issue.
The rubber gromets are very secure, compared to the Define, The HDD cage even without the thumbscrews are amazingly secure, so I didnt screw them in. I literally pulled at the HDD cage without the screw and it still wouldnt budge. The cable management is like the Define amazing, with tons of holes to route your cable through. Your 24pin cable to thick to make a sharp angle turn from the rubber gromet to the plug? Simple, route it through the gigantic hole between the mobo tray and the HDD cage. One huge difference between the Define and the Arc is that there is essentially two times more space behind the mobo tray in the Arc over the Define. which is a huge plus. Even adding a noise insulating foam by yourself on the Arc's panel would still provide a ton more space than the Define.
This is where the Arc shines and shines again. The case allows for a native 240mm rad that is 60mm thick without modding at the top. This only applies if your RAM isnt taller than the Corsair Vengeance. Why is this amazing you might ask? The more expensive 500r doesnt allow for such set-ups, the 650d doesnt as well (some people say it hits the side of the RAM). The Arc also allows for another 240mm rad at the front. This means that you essentially have enough space for a full dual 240mm loop INSIDE a case that is smaller than the HAF 932 with very little modding. However, this means that you will need to mount your HDD/SSD behind the HDD cage and you will lose the usage of optical bays if you are using sth like a XSPC Rasa kit. But who cares? A dual 240mm setup inside a mid-tower? Epic Win. Air flow is also pretty good with the stock fans. Keeping my GTX 580 Lightning Xtreme only 3 degrees higher than my HAF-X without a side fan. However, the anti-dust fan mesh isnt something I like. It covers the white front fans from being seen, and in theory allows less air to flow through them. What I am planning to do is to remove the mesh completely, while adding 140mm dust filters to the back of the front fans.
In contrast, the Define R3 doesnt allow for such W/C setups and also only allows shorter GPUs to be installed as it doesnt come with the removeable HDD cage. Well, it is targeted for silent computing, so it is fine. But such freedom should be present, as having a silent PC doesnt mean you need to be limited to shorter GPUs. This also due to the fact that much of its length is lost to the door, even though it is as long as the Arc (which allows a 580 Lightning Xtreme to fit in WITH the HDD cage on)
It is cheaper than the other mid-towers on the market by quite a bit, the 500r, the 932, the 650d, while providing very good build quality with plastic that looks identical to real aluminium LOL, and while allowing very big W/C setups in a small package. The only other case that exudes as much value in this price range is the 690 Advanced. But I prefer the styling of the Arc. So, if you wanna go with silent computing with a limit to how long the GPUs you have are and very little W/C potential as a trade-off, then the Define is good.
If you want, watercooling potential, "silent-enough" air cooling, allow for more GPUs, while having a sleek, doorless look, then the Arc is your go-to choice.
Personally, I am going to mod in a side-window, removing the side fan holes which I think is a great trade-off, considering the fact that, the case is also beautiful and the Arc just deserves one. Or maybe just cutting a CPU-exclusive acryllic window at the top. which will be great for a CPU-only loop.
Verdict for me in the end: Arc
This is a pretty long post, but I hope I did a pretty good comparism, If you have any questions, feel free to reply to this post or PM me about these cases.