You cannot go wrong!
There is a reason or many reasons why so many people love the 18's. If you really want to see it clean, get the newer style upper rack with the larger wash arm.
I think alot of the affinity for it was the fact that it provided classic cleaning ability that set the Kithcenaids apart from the rest of the flock but added the versatility that came from the additional wash arm under the top rack. That freed up the bottom rack to be used for pots,pans and dishes at the same time and still got all the dishware clean up top.
I have found one down side to many of theses 18-23 series machines, though, compared to the newer machines..
The newer machines with their super long cycles do tend to do a better job with the heavily encrusted pots and pans than did the K/A's of that vintage. You cannot clean a pan as well when you have the shorter wash times that the older machines had.
I must admit, however, that I did put a pot covered in dried on mac and cheese in my KD20-18-5 Frankenaid the other night on soak and scrub and with the 1400 watt element rewire job, it really heated the water to near boiling during the soak and that pot looked like it had just come out of the box, brand new, when the cycle was done. But that would be the exception to the rule.
You will love the 18 for sure, but it will sound like a truck compared to the Bosch I am sure!