Choices :s

Take a close look at the new Ultimaker 2.  It's single extruder, but high quality and fast.  Bukobot has a good dual extruder, but it is an open design, so better for PLA than ABS.  Also look at Flashforge Creator.  They are Makerbot clones with dual extruders, but in copying they also address problems that users had to overcome by modding their printers.  For size, some of the biggest printers are from thefutureis3d.com, which has a good reputation for service.

Something to consider it whether a printer uses an all metal hot end, or can have its hot end replaced with one.  That will give you more options for high temp materials like polycarbonate.

Most hot ends have a plastic portion leading up to the heated nozzle which can be ruined by getting them over 245C.  Some materials like Polycarbonate need to be printed at 250C, and also higher temperatures make it easier to print faster.  The faster the head moves, the faster the extruder has to push out the plastic, and the plastic flows more easily at higher temperatures.  With a hot end that is made completely of metal, you can go up to 300C without damaging it.  The open source, kit printers are more easily modded and tinkered with, so that is something to consider.

3D Systems charges $50 for .5kg of filament in chipped cartridges.  All other low cost printers can use 3rd party filament which is $30 for 1kg.  That printer is for people who think they can push a button and print an object without needing to learn anything about 3D printing, which isn't true of any printer under $10k.

Hyrel 3D has been experimenting with ceramic printing, but I don't know if you can buy one yet - http://www.hyrel3d.com/

The Flashforge is getting good reports. Since it's a (legal) clone of a Makerbot Replicator it benefits from the Replicator's popularity. So you can use the Sailfish firmware (a very nice enhanced "fork" of the open source Makerbot firmware), take advantage of enhancements produced by the community (e.g. machined metal extruders, replacement build plates, etc.). The only real "downside" to the Flashforge is that you're supporting a company that's basically copying someone else's work and cranking copies out cheap. It's entirely legal, of course, because everything in the Replicator is open and published, but they're not paying developers to work on improving the software, etc., which is something I like to support even if it costs a bit more. But in terms of what you physically get, it's a good printer, with two print heads, heated print bed, the ability to print ABS, PLA and all sorts of other materials, and (kinda) membership in the largest user community of any home 3D printer.

Both Ultimaker and Flashforge are made of wood, which is technically fine, but it would look out of place in an office, if that's an issue.

One thing I'd say is that huge print sizes on home 3D printers isn't generally useful. That is, to print a huge object you'd have to leave it running for days at a time, and there are good odds that you'd have some issue somewhere in the print so you're usually better off printing in more, smaller pieces and assembling them. Compare having to get a week-long print to go perfectly and restarting and running another week whenever there's any problem, vs. printing fourteen 12-hour prints, and any problem just meant reprinting that one component. One exception to this would be an extremely high speed printer, the QU-BD RXL which is just starting to ship, so there's a fairly long waiting list right now. They've shown videos (http://store.qu-bd.com/product.php?id_product=44) of 500 mm/s printing, and the results look quite good, and at that speed you could cover a huge area in a more reasonable time.

Note: I have a Replicator that I've been using for years, and have ordered a QU-BD RPM, which is a combination extruder and CNC mill, which I hope will ship in the next few weeks.

If you want to build yourself, it is much better to get a kit to begin with.  You will learn plenty from putting it together and working with all the components.  Building another from scratch would work better after you have some hands-on understanding of the parts and what is required of them.

oh and of course the REVOLUTION XL 3D PRINTER as mentioned above, that prints amazingly fast.
Bit of a smaller build size, but it seems to have a hot head suitable for 350 C and can print alot of materials

Ultimaker prints quite well. I like that company a lot, but I can't afford.

Nope. They haven't shipped a single one yet, and no one has ever see it mill anything.