I believe you are referring to the high falling tone. The high falling tone is merging with the high level tone in modern Cantonese, so you can merge them for most words. However, there are specific words (especially sentence ending particles) like 先 (\sin\) and 添 (\tim\) where they clearly are falling. Haih mh haih, \sin\? The main difference is the use of an "h" and diacritic marks with Yale vs. only using numbers with jyutping. And when Yale does use tone numbers instead of marks, the two systems match up. The other minor differences can be easily learned in in a matter of minutes. So, I would go with whatever you find easier.

As far as I understand it, both Yale and Jyutping systems have the same tones, including the low falling tone (tone 4): sī = si1 poem (high level - Tone 1) sí = si2 history (high rising - Tone 2) si = si3 try (mid level - Tone 3) sìh = si4 time (low falling - Tone 4) síh = si5 market (low rising - Tone 5) sih = si6 be (low level - Tone 6) I use a number of tools that use Yale with Jyutping tone numbers. For example: www.kodensha.jp/webapp/cantonese/can_converter_e.html and: www.mandarintools.com/dimsum.html I think eventually it will be beneficial for non-Chinese Cantonese learners to become familiar with more than one system. And since all romanization systems are ambiguous (i.e. same initial, final and tone but various different meanings), it is also good for Cantonese learners to learn how to read and write Chinese characters. Rob