How exactly was the finalist chosen in the NIST AES competition?
At the time of the competition (I can talk about it, I was there), there was a lot of discussion and various people showed arguments. However, there was never an official, publicly known "board of scores" with totals and definite rules, as the pictures you show seem to purport. It is possible that the NIST people did make something similar internally, but they certainly did not publish it. From the outside, the choice has been made by NIST in "some way" and they then provided qualitative reasons, not really quantitative. NIST never bound itself into following strict rules; they wanted to remain in control of the whole proceedings.

The picture still conveys the main reasons why Rijndael was chosen:


Its performance is nowhere bad. It was not the highest performer on every platform, but there was no platform where it would be abysmally slow, in contrast to almost any other candidate.
The "implementation difficulty" relates to features which, on some platforms, imply quite some work. For instance, RC6 requires a multiplier, which is hard on ASIC / FPGA (which translates to: it uses a lot of silicon space). MARS is very complex (many kinds of transforms piled up together) and implementers have reported that it took them quite some time to come up with working implementations, let alone optimized implementations. Twofish uses key-dependent S-boxes, which need RAM (bad for smart cards, bad for ASIC/FPGA). Rijndael was rather simple to implement (in retrospect, Serpent was better for that, especially if you want to implement the algorithm without lookup tables).


During the round conferences, where cryptographers who meet to talk about the AES candidates, some informal surveys were conducted, where people could give "scores" to candidates. While Rijndael did not necessarily elicit the best marks from everybody, nobody really hated it, so it looked fine as a future standard.



All of this, of course, depends on quite arbitrary assumptions on the usage context. NIST wanted an all-purpose block cipher, suitable to a large range of hardware platforms. If you target a specific system (e.g. for disk encryption on your PC), then this may point at another algorithm; for instance, RC6 is faster than Rijndael on a PC (except if the said PC offers the AES-NI instructions, of course).

The really good thing about the AES competition is not that it came up with a good, strong algorithm; what matters is that almost all candidates turned out to be good and strong. Among the 15 candidates, only two were "broken", and then only in an academic way. The trust we can have in AES comes from that: the AES competition proved that we apparently knew how to design algorithms that nobody else knows how to break (that's about as good as you can get with symmetric cryptography).