Ironically, I've ran all three of the bars you've mentioned, and with clip-on aerobars on each of them...
Enve SES Aero:
These are my favorite handlebars... I've got two pairs of the 35/40's on my road bikes, and then two pairs of the 37/42's on gravel type bikes. The flare is really nice for descending, and the hood transition is the best I've felt, for my Shimano Di2 levers. The clip-on aero bars are really solid, but do require some tweaking. The one piece, "cut to your desired length" extensions are just not great, and I swapped those out immediately, with something with a sharper bend. Due to the mounting position(and thus shorter length) of the extensions, you lose a bit of adjustability and I wasn't able to get some of the newer forearm shaped extension to fit. You also have pretty much zero ability to alter the stack of the arm rests, and if you do shim that, you are left with a fixed position of the extensions, so you can't get too extreme with that. I have sourced some 10d wedges from Europe that I have mounted under the arm rests, and combined with the 50 degree bend extensions, it gets me to a more "elevated hands" position comfortably. These will be my go-to for road use until I see something "better"... The Black Inc setup looks worthy of a try, but $800 is tough to commit to.
Pro PLT Ergo Carbon:
Prior to my first pair of the Enve SES bars, I had these on three bikes, and they were my favorite for a year or two. Again, they work really well with Shimano levers, creating a nice little platform at the back of the hoods for your palms to rest. I ran 36cm's on the road bikes, but had a pair of 38cm's on the Crux for a while, and did run some Profile Designs Sub Sonic Clip-ons on them. The 36's don't have room next to the stem, but the 38's just barely do. After usign the Enve's I grew to love the flare, and have since replaced all three of these with other bars.(I happen to have a set of 36's and 38's in boxes if you're interested)
Cervelo AB09:
I had a pair of the standard AB09 on a road bike for a while, and they were okay. I appreciate the simple routing via the deep groove underneath. This also makes for easy plug in of 11 speed di2 systems, as you can fit an extra wire in there out to the extensions and linked to a shift lever. They have a noticably longer reach than the above mentioned bars, and I don't love the feel of the transition to the levers. I now have the AB09 Flared on my Mosaic gravel/29er build. They are probably the "simplest" to mount clip-ons to, with the routing as mentioned, and a fairly generous width of clamping area. Again, I've only used Profile Designs Subsonic and Super sonic brackets, with a mixture of extensions and arm pads(the newer Ergo+ and Race+ are worth the upgrade for extra comfort).
I've only ran the flared model with GRX di2 levers, and they feel pretty good. The levers are a bit of a reach in the drops, but not horrible. I've done some pretty rowdy riding on these, with zero issues. The amount of flare feels appropriate for mixed surfaces, but would be too much for road use in my opinion, but that is obviously up to the riders preferences.
Other random one the Prime Primavera Aero, I ran these in the 36cm version, but they do/did? make a 38cm. No flare on these, so I came to the same place as I did with the Pro PLT's, in swapping them out for others.
I'll mention one other one that I just got in the mail two days ago...
Salsa Cowbell Carbon 38cm:
I'll be putting these on my Epic "gravel type build". I've had the 37/42 Enve SES bars on there, but this bike is built for some more technical type riding, and the longer reach and minimal flare has me wanting to try something a bit more compact and maybe with more flare... Just a theory, so I don't know yet. I definitely wanted to mainain the ability to add Clip-ons, as I foresee doing some FKT type 200+ mile routes on this bike. The Cowbells have like 100mm of clamp space for a stem and clip-ons. No internal routing, but this bike is now wireless, so only brake hoses, which tape against a flat spot on the front of the bar. These were less than $200, so worth experimenting, also lighter than the Enve's which was surprising...
