To help you choose a breed other then going for the looks (Which can be a reason too of course, but that needs little discussion) here are some numbers about the different breeds at various levels. Finally I'll go deeper into the lvl 220 skills to see if the top nanos can or cannot be reached.
Various "naked" skills (Maxed abilities and skills) :
Code:
LvL 100
Stat Solitus Nanomage Opifex Atrox
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BM 441 443 441 440
MM 441 443 441 440
MC 410 412 410 410
Health 1840 1328 1745 2269
Nano 2033 2683 1933 1388
Nanoinit 441 441 442 441
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Unlike many twinkers say breed hardly matters in what nano's you can cast. This is because the ability breed caps only start to count after LvL 150ish. Before that the only differences are the HP/Nano. You can also notice why Nanomage has a hard time around these levels because of the very low HP. Opifex and Solitus hardly differ, making the "but I can equip better QL implants" argument void. The existance of Temple Tubes also make Shades of Luc an unneeded item, further voiding the Nanomage's bonus in nanoskills at this level.
Code:
LvL 200
Stat Solitus Nanomage Opifex Atrox
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BM 719 727 715 699
MM 719 727 715 699
MC 659 664 656 645
Health 3197 2312 2992 3893
Nano 4167 5315 3952 3012
Nanoinit 719 718 731 707
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Here breeds are more noticably making a difference. Nanomage only gains a small amount of nanoskills (8 BM/MM and only 5 MC because of a lower Sta-cap) but its potential is higher with a Prof. Jones Vest. Not something everyone can attain though. Solitus gets roughly 900 more HP over Nanomage while Atrox roughly get 700 more HP over Solitus. The lack of nanoskills and nanopool is really starting to show for the Atrox breed here. At this level this is not a big problem; all nano's can be cast and it's not likely even a 200 Atrox runs out of nano casting the RK nanos. Opifex is jumping in lead with nano-init because of the high agility/sense caps at the cost of only 4 nanoskills (lower int cap).
Code:
LvL 220
Stat Solitus Nanomage Opifex Atrox
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BM 1294 1327 1290 1249
MM 1294 1327 1290 1249
MC 1134 1159 1126 1105
Health 4732 3362 4442 6013
Nano 6092 7935 5857 4282
Nanoinit 1294 1283 1331 1267
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As you can see breeds start to differ even more. Nanomage gains 31 nanoskills in BM/MM above Solitus while Atrox has no less then 45 nanoskills less then Solitus. Atrox gains a lot more HP out of this in return: 2650ish HP above Nanomage. Nano diffferences really do not matter at this level as everything is more aimed at nano-regen then at max nano. Max nano is only important / makes a lot difference at the TL4 (<150) and lower levels. In order to see what nanos each breed can and cannot cast we'll have to add proper equipement. To give a more realistic figure I did not use any loot from Pandenomium. I think it's safe to asume a LvL 220 character has a good symbiant set together with Inferno items though. Let's first add the best QL equipable symbiants (<QL250) and best perk choices for nanoskills (All primairy doctor perks with 10 Nanodoct, 1 enhanced DNA and 3 Genius).
Best Symbiants + Perks add:
+ 487 BM
+ 477 MM
+ 391 MC
+ 258 Nanoinit
+ 1339 HP
+ 1848 Nano
Best confirmed attainable items before Pandenomium:
http://auno.org/ao/equip.php?saveid=3772 (no bracers)
+ 209+10(abils) BM
+ 215+10(abils) MM
+ 167+11(abils) MC
+ 460+5(abils) Nanoinit
+ 1950+34(abils) HP
+ 1340+180(abils/pool) Nano
Adding buffs:
+920 HP (Superior Omni-Med Enhancement)
+1344 HP (Life Channeler)
+85 Nanoinit (Instinctive Control)
Total bonus:
+ 706 BM
+ 702 MM
+ 569 MC
+ 808 Nanoinit
+ 5587 HP
+ 3368 Nano
The Expensive Kevlar Vest of Professor Jones QL200 adds for nanomage:
+20-8(Azure BP) int = 2-3 BM/MM/MC
+20 BM/MM/MC
+50 Nanoinit
-250 HP (Azure BP)
Code:
Final stats:
Stat Solitus Nanomage Opifex Atrox
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BM 2000 2056 1996 1955
MM 1996 2052 1992 1951
MC 1703 1752 1695 1674
Health 10319 8699 10029 11600
Nano 9460 11303 9225 7650
Nanoinit 2102 2141 2139 2075
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Selfbuffed DOT's & Heal's:
Nanomage: Heal=Best DOT-A=Best DOT-B=Best DOT-C=Best
Solitus: Heal=2nd DOT-A=2nd DOT-B=Best DOT-C=Best
Opifex: Heal=2nd DOT-A=2nd DOT-B=Best DOT-C=Best
Atrox: Heal=3rd DOT-A=2nd DOT-B=Best DOT-C=Best
Composite-Infuse would be enough for Solitus/Opifex, Atrox would need Composite-Mochams
As you can see Nanomage with a +20 Prof. Horn Vest can cast the best heal selfbuffed without org contracts and Pand. loot. A solitus would have to try get 50 nanoskills from either (or both) in order to selfcast it, but it's possible for sure. Atrox however would always (as of now, perhaps we get better BM/MM items in the future) need outside buffs from MP/Trader.
Opifex and Solitus hardly differ. Opifex is less good then Solitus in everything 'cept nanoinit. It's however not a big difference; hardly any.
So what breed do you want to choose?
Level 100
Forget the nanoskill difference, they are near to none. Forget the ability colours unless you need to aim at IP costs at that level. The real difference is HP and Nano amounts. Do you want to be able to heal yourself (and others) more or do you want to be able to withstand more hits? Twink's usually would prefer more health while "levellers" may want to read further to see what the future brings to their breed.
Level 200
Only a small difference in nanoskills (Unless your a lucky nanomage with a Vest) and this hardly matters at all; every breed is selfcasting their nanos at this level. I'd even dare say a level 200 Atrox is the best breed if you want to stay 200 because you won't run out of nano anyways and enjoy more HP. I doubt there are many people that do not plan in levelling a lvl 200 character though. Because of the 1200 init-border the extra (or less) Nanoinit does not matter at all.
Level 220
A Nanomage would have an easier time casting the best heals in Shadowlands while an Atrox enjoys a bigger Health-bar (certainly useful to have in Shadowland when soloing). The choice between Opifex and Solitus would only be one out of looks then skills (unless you plan on using Tier3 armor who needs godly amounts of Sta). Funnely enough Atrox is the breed that will find it "easy" to equip QL300 Tier3 armor. With the amount of MP's running around (and the duration of their nanos) none of the breeds would mean "being a gimp": they all will selfcast the best nano with outside buffs. Add org contracts and you'll find it even easier casting the best nanos.