Use a combination of adhesives/solvents for the specific plastic you are printing with and mechanical joints or puzzle-piece interlocks between the component parts. You want a combination of increased surface area for the adhesive and a mechanical joint that strengthens the main axis that will take the most abuse.
Don’t forget you can also add apertures in the printed parts to mate with metal or plastic strength members to improve the strength of the part.
In the interests of providing some balance, don’t discount the Ultimaker. Make magazines roundup that included the bukobot rated ultimaker top for speed and accuracy. Although it’s quasi-closed source, it doesn’t prevent you hacking and there’s a large community of Ultimaker hackers out there. Several people have done dual extruder hacks for instance.