I personally use the Grand. Was an Arabella but has now been refurbished (late last year) and is a Westin. Right by the central shopping street Zeil. IMHO the Grand is miles ahead of the Meridien.
Catch the S-Bahn from T1 at FRA to Konstablerwache station or get a cab from FRA.
PS have a look at Tripadvisor for Hotel comments and the Frankfurt Tripadviser forum for train fares etc