Here are some thoughts...
I really like having a 3 gallon better bottle around. It's easy to move around and it fits inside my bottling bucket if I'd like to put it in an ice bath at the beginning of fermentation. It's where I try out new recipes before brewing a bigger batch. Now I have 3, 5, 6, and 6.5 gallon carboys to choose from, so I have some freedom. I understand that might not be reasonable when you're just getting into the hobby.
My outside-the-box alternative for you is to get 2x 3 gallon better bottles. That way, if you're creating your own recipe, just scale down to 3 gallons. Then, when you use a 5 gallon pre-packaged kit, just split your wort into 2. As a side note, this would easily facilitate some experimentation (diff yeasts, dry hopping, etc).
Anyway, whatever you do, good luck and happy brewing!
JRBrewer on Untappd
Planned - GP/Mosaic SMaSH
Fermenting - Ned's Red (Flanders Red Ale), Saison Graf, Tangerine Mead
Bottled - Belgian Tripel, Belgo Graf, Saison (split batch with brett), Black 13 (Graf Porter), Old Style Amer. Cream Ale, Amber Graf, Wheat Graf, Bannockburn Wee Heavy, Berry Mead