Accommodation used by ScotRail on longer journeys between Aberdeen, Inverness and the central belt came under cricism from Maureen Watt.
The Aberdeen South and North Kincardine MSP made the comments during an inquiry at the Scottish Parliament into the future of the franchise from 2014.
It follows a consultation on the way the network operates, including potential changes to cross-border transport, the sleeper service and rolling stock.
Ms Watt said: “From Aberdeen, people who are not time-constrained will opt to take an East Coast mainline because it’s a better type of carriage.
“Why can’t we be urging ScotRail to say, ‘actually from Aberdeen and Inverness to Edinburgh and/or Glasgow it has to be a different type of train that’s more comfortable and more suitable for a longer journey’.
“Because, quite frankly, the type of carriages they’re running at the moment are horrible.”
The comments were made in a wider inquiry, with views from passengers’ groups.
John Brandon, convener of the Friends of the Far North Line, accused First Minister Alex Salmond of failing to keep a promise to upgrade railway lines.
He said: “The 2008 strategic transport review promised there would be an hourly service on the Highland mainline with improved journey times.
“That was confirmed by the First Minister when he visited Inverness that this would come in in the December 2011 timetable.
“All we got in the timetable was two extra trains. Because there were no infrastructure improvements and we’ve got long stretches of single line on the Highland mainline, it has actually had a deleterious effect on journey times, and will do unless the infrastructure is improved.”
The ScotRail passenger rail franchise was awarded to FirstGroup in 2004 and will run to 2014.