If dates matter, that may narrow things down a bit.
The Exactrail / Front Range/ McKean 63' Centerbeam was first produced in 1977.
https://exactrail.com/collections/thral ... m-flat-car" onclick="window.open(this.href);return false;
The Walthers 73' Centerbeams were first produced in 1987
https://www.walthers.com/search/mode/li ... Centerbeam" onclick="window.open(this.href);return false;
The Atlas Center partition (Centerbeam)
http://www.atlasrr.com/HOFreight/ho73ce ... ition1.htm" onclick="window.open(this.href);return false;
Since I lean toward the 1970's and early 1980's, I prefer the 63' Centerbeams and added the very nice ExactRail cars (BN, UP, MILW & WP) to my roster. Only MILW & WP are left in stock but worth getting and very nice. I don't know if ER will ever produce them again.
Probably the most economical of the lot are the Walthers - which can be had for as little as $20 if you hunt around - but more go in the $30 and higher range.
The Atlas and ExactRail are pricier - but more detailed. Again, shopping around can help minimize cost. Ebay has some nutty prices that should not be rewarded just because items are harder to find, people ask 2x the MRSP. Be patient and watch for the better deals, visit train shows etc.
If you are on a budget, Front Range & McKean kits can be had for cheap; the trade off is they are a bit of a challenge to build - you'll have to do some filing and work on the parts to get them to fit well, but results can be a decent model. I have a Front Range WP car I built from a kit but have replaced it with the ExactRail version - the body is assembled but some parts need to be glued on as well as decals applied. It came painted dark blue but in reality the cars were black so I airbrushed mine black.