NOT-ADVICE of course
As with
@UltradoomY and his response, I'm a fan of the larger spread sizes; $100 over $25.
What I learned with personal and painful experience is that with a $25 spread size, the shares can go from max gain (OTM on the short put) to max loss (ITM on the long put) in seemingly a flash. In my case it was a $20 spread size that I finally closed for 40-70% losses (a few different instances, closed at different times). I use the term 'travel' in my mind - as in how much travel do I have between full gain and loss.
I want my BPS to behave much more like short puts and I want to restrain my own tendency to keep getting more and more aggressive as my positions win repeatedly. So far the $100 spread size is doing that for me, though I haven't yet gone ITM and needed to roll these. I'm also trying out a $80 spread size right now, where my hypothesis is that with IV shrinking a smaller spread size will work well. I would expect the corollary to be true - if IV jumped a lot I would probably start going higher than a $100 spread size.
The relationship I have observed - the larger spread sizes provide larger absolute net credits while also providing smaller % net credits relative to the spread size.
IMHO - these spreads should best be viewed and treated as leverage. The margin reservation on a $100 spread size is $10k. I can open 6 of these for the same cash security for a $600 put (on short puts I've restricted myself to positions I can take assignment on in full without taking a margin loan to fund them). That is 6:1 leverage. It might be closer to 3 or 2:1 if I were selling puts on margin.
The point here is that these are all leveraged positions and carry with them the need to treat them with more respect; losses will build faster, just as gains will build faster.