Another vote for the Hybrid line. Yes, they are durable!
I have any sort of pad you can think about, Meguiar's line (foam and MF), LC flat, CCS, hydro-techs, and hybrids. Sure I have others I forgot to mention.
However, just after using Hybrids for the first time, I can't think of another better combination for the flex 3401. I'm to re-order some pads, and they will all be from the Hybrids.
The 6.5" pads goes just right into the standard backing plate.
To use the smaller pads (5") you'll have to get the LC changeable backing plate system.
I recommend you to get both 6.5" and 5" to tackle an entire car with all curves and details.
The Hybrid Wool pad is an 'Ultra-Heavy' cutting pad, yet it can finish down great even on black color. However, it would benefit of a secondary polishing step.
Basically, after cutting with Wool pad + FG400, 3 fast passes with SF4000 and White pad will give you a 'more than show car' finish. Guaranteed!
The Orange pad is incredible because paired with FG400 (A heavy-cut compound) it can get rid of heavy defects yet finish down LSP-ready in many cases, without needing / benefiting of a secondary step. It's the pad I use most.
PS: To achieve perfect cut and finish with Orange Hybrid + FG400 you have to use some technique like recommended by Smack (Mike). It takes more passes than a normal compounding step, it's just like a compound + polishing step altogether. Instead of doing 4 passes with compound, switching pad and product, doing 4 passes with polish, you just do ~8 passes with FG400, reducing pressure (I also reduce speed) for the last passes.
The Blue pad is light cutting but also finishes down great. I don't use it very much because when I need the blue I just use the Orange at lower speed / less pressure... I've also noticed blue pad durability to be worst than other hybrids, reminding that low durability of Hydro-Tech Cyan (looks like same foam?!).
The White pad is a 'Classic Polishing' pad, it's as good as any LC white pad but have the 'Hybrid' feel, and that means a beveled edge pad that helps you to achieve uniform pressure distribution and smooth polisher movement. Very durable, but beware of the pad conditioning brush. It's better to brush this pad with the polisher off instead of running the pad while brushing it. The orange pad resists speed 6 brushing without any harm.
The Yellow pad is a light polishing pad, yet it feels more dense than the cutting pad from the hybrid line. It's tricky to use, and it's not a pad you'll reach very much. It's interesting pad, indeed.
The Black/Gray finishing pad... Well... I'm an 'idiot' because I've thought my actual flat / CCS pads would be ok and I would not need a Gray Hybrid. I've regretted not ordering any Gray Hybrid Finishing pad, but they'll be in my next order for sure.
That said, I would get:
1 Wool Hybrid Pad - For fast heavy defect removal
2 units 6.5" Orange Hybrid - For general Cutting / 1-step
2 units 5" Orange Hybrid
2 units 6.5" White Hybrid - For general Polish / 1-step
2 units 5" White Hybrid
2 units 6.5" Gray Hybrid - For finishing polish / LSP application
2 units 5" Gray Hybrid
Please, feel free to agree, disagree, and comment on your final choice.
Like I've said, I'm getting more pads for my 3401 and any input will help me as well.
Hope I've helped,
Kind Regards.