Overlapping units with BT

Hey everyone! I'm planning to go for Dark Angels or Black Templar as my next army, but would like to try out my ideas for color schemes first, and see whoch one I prefer and then buy that army's Combat Patrol.

I wanted to ask if there are any overlapping melee units that I could buy one of and then paint one model each as a Black Templar / Dark Angel?

I wanted to buy the Bladeguard unit first, but then saw a video that said it wasn't very useful in a Black Templar army (and I'd get another such unit in their CP).

So now I don't know which unit to get. I could get intercessors, but I get those in the DA CP anyway, plus I'd really like to test the scheme on a model with swords. I feel like I always circle back to picking the Bladeguard, but it would just be so dumb if I won't need it should I choose BT, so I wanted to ask for help in case any of you have an idea.