Help replacing old Apollo Hydroheater

[hodge12]

Replacing old nat. gas Apollo Hydroheat 50gal in improved 1,500sq ft. ducted basement. EnergyGuide reads: "First hour Rating 98 - Model(s) A5 50 65.ONQRT8 5FJ - Only models with first hour rating of 87 to 99 gallons are used in the scale." Got a good plumber but he's never even seen an old hydroheating system before viewing mine. He recommends an AO Smith with first hour rating 93 - Recovery rate 90degree = 67 - energy factor .058 at 65,000btu input. This GCVX50 is replaced by GCRX50L which has first hour rating 98 - Recovery rate 90degree=61 and energy factor .060 at 60,000btu input. Which one would work better or is there a water heater model better suited for replacement? Advice appreciated.