I have only been growing for a few years, but from all I have read here, you do not NEED to prune the Betterboy. Suckers will bear fruit, I have read. Some consider them branches, a more positive term.
Perhaps a search under To Prune or Not to Prune would assist you. Or Pinch? Or maybe, Suckers?
There are a lot of threads about all these matters. Good luck!

Sorry but there is no way to tell them apart at this stage as leaf type is the only distinguishing characteristic and those varieties are both regular leaf.

Eventually you will be able to tell simply from the size of the plant and the shape of the green fruit but that is a ways down the road.

As already mentioned, pruning is not required, just optional. So until you get fruit set and shape to tell which is which, I'm afraid you are stuck.

Dave

Thanks for the replies. So Betterboy and Roma both can be left untouched - no pinching or pruning ? I know that's the case for Roma but Betterboy also ?

There is no need to pinch or prune Better Boy. As digdirt said, it's optional, not necessary at all. The "suckers" are not parasites; they are fruiting branches and they will produce blossoms and fruit.

I would wait until the first fruit sets and treat them the exact same until then. Roma's and Better Boy's are quite different looking tomatoes...

Thank you all for your help.