Saying Shema prior to sunrise:
When Davening in a Vaasikin/Neitz Minyan: The initial time for Davening Shemoneh Esrei is by sunrise. It is a Mitzvah Min Hamuvchar to read the Shema slightly prior to sunrise, intending to complete the Shema and its last blessing of Goal Yisrael with sunrise. Immediately upon finishing Goal Yisrael by sunrise, one Davens Shemoneh Esrei, thus accomplishing the approximation of Geula to Tefila, and the Davening of Shemoneh Esrei by its initial time of sunrise. One who is able to do this [finish Goal Yisrael immediately by sunrise and then Daven Shemoneh Esrei] receives great reward and is guaranteed a portion in the world to come.
When not Davening by Neitz: Some Poskim rule one is only required to read the Shema before sunrise if he plans to Daven Shemoneh Esrei with sunrise [Vaasikin]. If however he is unable to say Shemoneh Esrei exactly by sunrise then he is not read the Shema and Daven before sunrise and is rather to read it after sunrise upon Davening. Other Poskim however rule that Shema is initially required to be recited prior to sunrise, irrelevant as to the time one plans to Daven Shacharis. Hence, one should always say Shema before sunrise even if Shemoneh Esrei will only be Davened after sunrise, and one will be unable to proximate Geula to Tefila. Practically, although the main opinion follows the first opinion, nevertheless it is proper to suspect for the latter opinion and to read at least the first Parsha of Shema prior to sunrise [even if he will only be Davening after sunrise]. This applies even if one has not yet worn Tallis or Tefillin. Upon later Davening after sunrise one is to read the Shema with its Brachos as is regularly done.
It is a Mitzvah Min Hamuvchar to Daven Vaasikin and recite Shema and its blessings slightly before sunrise and then Daven Shemoneh Esrei immediately by sunrise. Even one who is not Davening Vasikin is to recite at least the first paragraph of Shema before sunrise, even though he does not plan to Daven Shemoneh Esrei at sunrise and is not wearing Tallis and Tefillin, and will thus only Daven later on.
 58/4; Ketzos 19/12
 Admur ibid; Michaber 58/1
 The wording here follows the first opinion mentioned next and rules that the reason behind Vaasikin is for the purpose of Davening Shemoneh Esrei at sunrise, and is not due to any obligation of when to recite the Shema.
 Admur ibid in parentheses
 1st opinion in Admur; Michaber ibid which rules the Davening of Vasikin is only a Mitzvah Min Hamuvchar; Majority of Rishonim in Brachos 9b; Rashba; Tosafus Yuma 37b; Rosh; See Rashi ibid and 26a; Megillah 23a
 The reason: This opinion rules that the purpose of reading the Shema slightly before sunrise is only for the sake of Davening Shemoneh Esrei by sunrise, [after approximating Geula to Tefila], and is not due to any obligation to read Shema before sunrise. Thus, if one in any event does not plan to Daven Shemoneh Esrei at sunrise then there is no purpose of saying Shema before sunrise, as Shema may even initially be recited until the 4th hour of the day. One is not to say Shema and Shemoneh Esrei before sunrise, as one is initially to Daven Shemoneh Esrei from sunrise and onwards and not before hand. [ibid]
 2nd opinion in Admur; Ramban in Milchamos; Rabbeinu Yona 9b; See Rashi ibid and 26a; Megillah 23a; Rambam Shema 1/11; Peri Chaadash; See Birkeiy Yosef 58/2; Vetzrauch Iyun why Admur does not mention the Rambam as one of the sources of this opinion
 The reason: This opinion rules that the reason for Davening Neitz is not only to say Shemoneh Esrei with sunrise but additionally in order to recite Shema before sunrise. The reason for this is because one is to initially read the Shema at a time that majority of people awaken, as majority of people awaken prior to sunrise, as only the princes arristocrtas and the like waken after sunrise. [ibid] The Rambam ibid and other Rishonim who rule like him hold that the reading of Shema after sunrise is Bedieved, and the entire Mitzvah is for it to be read before sunrise.
 Admur ibid; implication of Beis Yosef; see M”A 58/3; Siddur Yaavetz; Ashel Avraham Butchach 25; See Piskeiy Teshuvos 58/5
 Admur ibid; Levush 58/2; however see Kaf Hachaim