Whoa, I'm holding up a mod. O_O Better post, eh? XD
Let's see...my absolute favourite fossil pok?mon...need you ask? Cradily of course. *Huggles Cradily* Not only is it the most adorable little bugger of the lot (Come on, it's carnivorous, it's green, and it's got that lovably hungry smile on it all the time XD) but it would also pwn any other fossil pok?mon in a one-on-one;
Cradily vs Kabutops
Kabutops is completely Giga Drain pwned. Also, if it's a physical attacker then Cradily can completely swamp it with Barrier, if it's a spec. attacker the Mirror Coat combined with Cradily's high Sp.Def will give it a fast and painfull end.
Cradily vs Omastar
See above. It might take longer to take down Omastar, but I'm afraid that there's very little the poor thing can do against a triple-Amnesia Cradily. Giga Drain and Earthquake would drop it eventually, another option being hitting the Omastar with Toxic and then stalling it out with Recover and Amnesia.
Cradily vs Armaldo
Rock Slide pwned. The strongest super effective attack that Armaldo can muster against Cradily is Hidden Power [Bug], assuming it has maximum IVs. But once again, Toxic, a triple Barrier, and Recover stalling would KO the opposition.
Cradily vs Aerodactyl
Triple Barrier and Toxistalling all the way, possibly with a few Rock Slides for good measure. A CB Aerodactyl could provide some trouble, but a properly fortified Cradily should be able to shrug the damage off. This one is perhaps the greatest treath but by no means unbeatable.
Yup, Cradily pwns, although it's movepool is a tad limited in certain areas. During my unenlightened days, I ran into one in NetBattle that massacred my whole team, I'm not making the mistake of underestimating it twice. No I'm not. Plus, it's my favourite! *Huggles Cradily again*
But since I don't feel like being too unfair, I'll point out the pros of the others too, because they're all tough;
Armaldo
High Defense and Attack stats and a fairly average HP. Despite it's Steel/Rock weakness Armaldo isn't a half bad physical tank, the best approach is probably to concentrate the EVs and nature on its Defense and HP and then give it Swords Dance to boost up its damaging potential. Armaldo also enjoys a somewhat better movepool than Cradily and the ability to learn moves like Rock Blast and Brick Break should by no means be underestimated. Plus, it can also learn Rapid Spin to take care of any nasty Leech Seeds or Spikes heading your way. It's rather vulnerable against special attackers though, especially with its low Speed and Water weakness, so I don't use Armaldo too much myself. It's not a half-bad pok?mon though.
Aerodactyl
Pwhee for the most overused fossil pok?mon in existence! Aerodactyl has very high Attack and Speed stats that have made it one of the most common physical sweepers in Netbattle. Since its defenses and HP aren't that great, the prefered fighting method with Aerodactyl is strike fast, strike hard and they quite often carry Choice Bands, with EVs and nature geared towards Attack and Speed. The ability to learn both Earthquake and Rock Slide gives this flying type a considerable advantage towards the type's classical weaknesses; Electricity and Ice. Certainly a tough pok?mon by any measure, and by far the most popular.
Omastar
Quite badly overshadowed by Aerodactyl, but a fairly common choice for UU teams. Omastar's statline is very heavily based on Defense and Sp.Attack, making it a good counter against physical sweepers. Unfortunately, its Sp.Defense and HP are mediocre at best, which, combined with its double weakness against Grass and its normal weakness against electricity, make it pretty much a sitting duck against any competent special sweeper. However, Omastar is capable of having the Swift Swim trait, which, activated in combination with the right EVs, can actually make it faster than quite a wide range of other pok?mon, allowing you to take down quite a few opponents, who thought they were faster, by surprise. It is also capable of learning a lovely little move called Spikes, so Omastar is quite a multi-purpose pok?mon; Spiker, Tank, and Sweeper, although it doesn't particularly excell in any field. I think the biggest advantage of Omastar is that your opponent will never be able to be sure which of the approaches you have taken.
Kabutops
Unlike Omastar, Kabutops is geared towards physical attacks, with Attack and Defense being its highest stats. It also has a distinctly offensive statline, with higher Speed but lower defenses and HP than Omastar and is probably best suited to be a physical sweeper. With a quite formidable 70 as base Speed and the right EVs and/or Nature and the Swift Swim trait Kabutops can outspeed a great deal of pok?mon, which, combined with its high Attack, makes it quite lethal in battle, although Aerodactyl performs better in this respect and doesn't need one turn of charge up, which has consequently knocked Kabutops down to being an UU as well. Kabutops' biggest weakness, much like Omastar's, is that it has very poor endurance against special attacks which often gets it KOed quickly in battle. And while it's capable of learning some counter moves towards its weaknesses (Aerial Ace against Grass and Fighting types and Mud Shot against electric types) they don't really have that much power to them and as such, often fail to provide the one-hit KO that Kabutops so desperately needs. One thing that annoys me about this pok?mon is that it learns the whole HP draining set of Grass moves (Absorb, Mega Drain, and Giga Drain) but lacks the Sp.Attack to make anything useful out of it. It is also capable of learning Rapid Spin, but lacks the proper defenses to really act as a Spinner. It's not too bad as pok?mon go, but I'd say it's still the weakest of the lot.
So yeah, I think that's all I have to say for the moment. Since I'm taking this from the perspective of fighting potential I obviously haven't included the first stages of any pok?mon because they learn exactly the same things, just a bit faster. And it's, of course, completely okay to like/love unevolved pok?mon too (Lileep ish kawaii ^^) but that doesn't mean they'll be much good in battle.