please say your opinion what's better PR4 (5 year old domain indexed by google) or PR5 (1 year old domain indexed by google) ?
At first glance, the five year old domain. A pagerank difference of one isn't likely to make as much of a difference. A four year gap is something though. Do they both contain the keywords that you want to rank for ?
IMO. neither PR nor age will make a major difference. One needs to see the quality of backlinks to determine the value of a domain.
I'd take that older site. There are a variety of methods to get a site up to PR5 in 1 year, but no methods to make the domain older.
This is a difficult one to answer. At first view the 5 yr old site sounds better, but then if the 1 yr site has got far more established and relevant links for your market then it could be better.
To many factors....Domain name, popularity, is it in any good directories like yahoo, BOTW, DMOZ...But to be honest page rank really doesn't mean a whole lot but age does..