Semi Sextile is Berlin Wall and not the best nor worst position, it is the third worst position you can get. Unfortunately you can not get all of your signs 100% Trine with someone, or at least I have yet to see it. Semi Sextile is Leo with Cancer and Virgo. Trine is the best and Square would be worst… Opposing along with Conjunctions are truly the last position I would consider. Fire and Air together, Earth and Water together; any other exceptions are really inadvisable. This is in looking for a partner or friends, not looking at aspects in you own chart; that is different.
The trine(120°) is the relationship of one sign to those four signs away from it on the wheel(such as Aries to Leo, or Aries to Sagittarius), and the sextile(60°) is the relationship of one sign to those two signs away on the wheel(such as Aries to Gemini, or Aries to Aquarius). Both the trine and sextile are considered as non-critical or secondary aspects because of their generally easy or free-flowing natures. This however, does not make them any less important than the first group. It would be like saying that the signs of Gemini and Aquarius (representing the sextile) and Leo and Sagttarius(representing the trine) are less important than Aries and Libra(representing the conjunction and opposition respectively) or Cancer and Capricorn(representing the square). In astrology no one sign is any more important than another and therefore neither should any of the aspects be either.
To complete the horoscope the astrologer will look at the aspects or relative angles between pairs of planets. Certain aspects are considered more important than others. Those generally recognized by the astrological community are Conjunction (0°), Opposition (180°), Square (90°), Trine (120°), Sextile (60°), Semi-Sextile (30°), Semi-Square (45°), Quintile (72°), Sesquisquare (135°), Bi-Quintile (144°) and Quincunx (150°). Astrologers claim that these aspects function within an orb of influence, the size of which varies according to the importance of each aspect. Thus conjunctions are said to operate with a larger orb than sextiles. Most modern astrologers use an orb of 8° or less for aspects involving the Sun, Moon, and Jupiter and smaller orbs for the other points. Some astrologers, such as practitioners of Cosmobiology, and Uranian astrology, use minor aspects (15°, 22.5°, 67.5°, 75°, 105°, 112.5°).