Creating a read only replica of SQL Server database for reports
Does Transactional replication suit my problem the most among SQL
  Server replication mechanisms?


Out of all of the replication options - Transactional sounds like it is what helps you the most here. It gives the minimal latency and it doesn't need to be (but can be) bidirectional. You aren't merging changes and don't need Peer to Peer.

That said - Replication isn't "free" -  you need to administer and monitor it and a poor setup could make performance problems worse. You should learn about the best options for performance and the best setup for performance and keep that in mind and keep your replication environment monitored.

Transactional replication is "easier" than Merge replication. But that doesn't mean you will always have a smooth sail and can always get away without someone with replication experience helping out.


  If I have an opportunity to migrate from SQL Server 2008 to SQL Server
  2012 would transactional replication have some breaking changes? I've
  read an article on technet that there might occur errors?


Unfortunately this is an "it depends" type of question. We could theoretically give you answers from our own experiences, but you will need to test. If you do bump into issues they will not necessarily be impossible issues that you cannot fix, they will require testing and tweaking.


  Isn't SQL Server 2012 Always On mechanism better to solve my
  problem(I'm considering this option as last one, as I'm still using
  2008 R2, and yet migration to 2012 is planned by not soon)?


In SQL Server 2012 AlwaysOn has something for you here that works potentially. Availability Groups are an answer here with the concept of an Active Secondary for reading purposes.  But there are licensing concerns - you need to be in Enterprise on both the primary and the read only/active secondary. With the replication approach you still need to be licensed on both ends, but this is a good option for sure. It, too, has overhead associated and some administrative concerns that you should learn about - but it makes a great option.