All depends on what liquid I'll be putting in them and what my vaping budget is for the month
CE2/Fluxomizer/Visions...on an eGo I like the lower resistance ones from 2.4 to 2.6 Ohms.
Airy/easy draw
Warm feeling vape even at lower temperatures.
Moderate to soft throat hit.
Superb vapor production for a single coil (and to me these work best at lower voltages).
Great flavor when set up properly.
If it's a nice strong flavor I really like the Giant Vision CE style carto. These are large like Giantomziers, but the mouthpiece and all the top seals are designed totally different. No tools are needed to fill a Vision...just pull off the top and drip in your liquid. Visions also come in smaller sizes which are slightly more flavorful, but I love the honking 3+ml capacity of them. I like to mix my liquids ever so slightly stronger for these, and stick with liquids with no more than 30% VG. The Visions last long enough to chime in at way under a dollar a day to own and operate them. They also make an even bigger 5ml Vision 'tank' now...I haven't tried one yet.
Stock CE2/Fluxos/Giantomizers by MiT/Royal Smokes require tools or special bottles to fill, or need to be modded if you don't want to mess with needles/pipettes. For some liquids you might want to mod the CE2 for better wicking. A first time set up then it's pretty easy from then on. The regular size CE2 and the XL sized ones are a great value. Five to a box, and they usually last for many many hours/days/weeks of regular vaping (of course they'll need to be refilled fairly often).
Bud Sapphire
Moderate throat hit
Medium Draw (tigher than a CE2 for sure, maybe slightly tighter than a 510 atty or brand new vertical coil (like the Boge) but much much looser than say an eGo T). The LR ones are nice and warm on an eGo.
I have a couple of flavors that I vape for a few minutes maybe twice a week. These flavors actually vape very well in the Buds that I've tried. These are really easy to fill, but there are a couple of parts that have to be pulled off and put back on to refill (no tools needed but if you have really large hands/fingers or limited dexterity/eye-sight it might be PITA) and they only hold about 1.5ml. For me...it doesn't take long to vape one dry. I like them enough to keep some in my stash and I do use them often, but they're just too small to be my main goto carto.
To me Polyfill cartos have a stronger throat hit. New/fresh out of the box the flavor is great as well but declines a lot faster than with the wick based stuff. So if throat hit is your thing...read on.
My all time favorite poly-fill type carto on the eGo for almost any liquid, even thick pure VG are the LR (1.7 to 2 Ohms) 801/302/510 hybrids (or even an 801/302 with an adapter). Nice over-sized coil in a horizontal configuration. These aren't always available and don't come cheap though (I've gotten them from Ikenvape and sometimes Nhaler carries an equivalent...801/302 carto on 510 threads).
Now with bigger batteries that can crank up the voltage and still last most of a day, I'm all over the Boges and SmokTech dual coils. For me they do require pretty constant rewetting, so get a drip tip and carry a bottle of liquid with you if you vape pretty heavily and like the vertical coil cartos. Set them in a cartomizer-tank (requires 'punched or slotted cartos') and they're really nice.
These days there are all sorts of eGo sized poly-fill cartos as well. Both single and dual coils...both horizontal or vertical. Give some a try...just be aware that the dual coil stuff might draw your battery down pretty quickly.
To me the poly fill cartos do have a stronger throat hit than anything wick based.
Honestly, it's all seriously subjective. Different liquids perform/taste different in all of the cartos. You'll just need to try things for yourself over time. I learned long ago not to seriously 'stock up' on one particular thing because it seems every couple of weeks something new comes out to try (plus alot of it lasted longer than I thought it would). Break up a box of cartos and hit the PIF forum and swap things around if you're not made out of cash. Also stick around ECF as vendors are always running contests and games where you can try things for free or really cheap.