Latitude & longitude universal format I don't know yet what database I'll use in the future - MySql, Postgresql, Sqlite3 or anything else. At the moment I'm using a database N.

What's more or less universal approach for storing latitude &amp; longitude? Varchar? Or big integer? Or float? 

Should I store them in 2 columns or one?
Neither. The right answer is to use the GIS Spatial Type for a point. All of those databases have their own implementation.

PostgreSQL's PostGIS is easily the most full featured GIS implementation,

CREATE TABLE foo(
  gid  int GENERATED BY DEFAULT AS IDENTITY,
  geog geography(POINT)
);


I would highly suggest going PostgreSQL, and checking out the book PostGIS in Action if you're new to this.
See also,


My comparison of MySQL and PostgreSQL's PostGIS for spatial 
MySQL Spatial Data Types (which suck btw),
SQLite Spatial Extension SpatiaLite