It’s also worth noting that the first two patterns come in traditional bra sizes (band + cup) while the latter two come in S/M/L/etc. This affects both the design and fit of the final bra.
Watson is an awesome starter bra pattern. The instructions are easy to follow — including walking you through unfamiliar techniques and giving guidance on stitch width and length — and you end up with a nice bra. In terms of wear, it’s comfortable, though not the most comfortable on my list. I’ve also had some “muffin top” in the cups which are related to fit issues/being pregnant, but are still more of an issue here due to Watson’s cup shape.
Harriet is the bra to be proud of making. It’s more complicated to sew, but still has Cloth Habit’s accessibility in the style of directions. Sizing on Harriet is key. Once I made the bra in the correct size, it was comfortable (though a different comfortable than wearing a non-underwire bra). If you’re looking for an underwire bra pattern, this is a good one to check out.
Barrett is the bra I both love and hate. I hate putting it on (it’s a pull-over with no back fastener) but, once it’s on, it’s the bra I’d rate as most comfortable. I also wasn’t a big fan of the directions, which were very text heavy and didn’t have clearly enumerated steps; I definitely wouldn’t make this as your first bra. That said, this is a free pattern and could easily be modified to include a back fastener.
Romy is an all around solid pattern. Good directions (though lacking some of the extra details of Watson) and a comfortable wear. I also like the finishing detail in the enclosed seams. I think Romy is more forgiving of fit issues, likely due to the cup shape. I really like my Romy bras, with the exception that the back straps need to be closer together.
All told, if you’ve never sewn a bra before, sew a Watson. Otherwise, try a Romy or, if you don’t mind a pull-over, a Barrett. For a good but accessible challenge, tackle a Harriet. I hope this comparison helps!