<< heheh...my sis-in-law is an english major...
GrammAr is the correct spelling, and neither is correct. Not just for having "but" at the beginning, but there is really no such word as "nicer", again, according to her. She suggests using "better" in place of "nicer".
nice
adj. nicer, nicest
source - Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
And nowadays starting a sentence with but is somewhat acceptable. "Everything looks nicer than it really is" would be better, depending on the context.
For some reason is at the end is bugging me
Than and grammar are correct.