Or a large asteroid.
Edit: Some get really big, getting it there, and getting it out of the way if allied ships are coming through would be a problem though, well, so would many of the other booby traps too.
In relation to the origianal question. I think the collie is a complete and utter... a slight success. It can take on multiple destroyers very well, it even did most of the work in taking out a sath (but alpha 1 made it do it without getting a day of damage, but stupid command had to make the reactors overload!!), it could take on lucy's coming as fast as possible out of a node and has "More firepower than 5 orion class destroyers combined" (apparently) and has twice the htps. When it looked down the barrel of a sath the captain could of thought, oh yeh, bring it on, i've already taken on one of yous and it was easy (thanks to alpha 1), i've already taken out your ravana, lets see how much of a fight you can put up!! A terrible underestimation. It was taken out in seconds. it was a success at what it was designed to do at the time of building, the GTVA could never of guessed a warship bigger than it and so much more powerfull could have existed. As far as they knew, demons and lucifers were the bigbomberuchies (pronounced big-bomb-ber-uchie), if they had thought the shivans would come in greater force they would of been correct, and to all they knew the collie could handle that as well, but an enemy could be infinite in power if you try to plan bigger, the enemy will always be more powerfull than you if you think about it, you'll never get a warship that can take of an infitey powered warship, never!! So they had to guess at what the shivans could come up with, sadly, they were a bit more powerfull then their estimation, and come on, the juggernaut armada was hundreds of times more powerfull then the lucy fleet. How do you plan for that, the collie could take on something say, ten times more powerfull with the help of alpha 1, but you have to draw the line somewhere.
A small highly powered corvette/destroyer (like a frigate) would be the ideal option, but if you get bigger, you need to get a few, lets hope the terrans have learned not to put all their eggs in one basket, put them in a couple. Sobeks are great, they can handle decent punishment, and can give out fantastically for their size, a terran version of that, perhaps a corvette or frigate centered around a LRBGreen or BFGreen with moderate to low Flak and aaa cannons and what's left could be put into armour (no fighterbay) would be a good anti juggernaut warship, cheaper than a collie and many times smaller you could make several of them and be able to take out a jugg more efectively than a collie. Make other ships that carry the fighter support, like a non moving carrier with severely limited anti-warship weapons but good flak/AAA coverage and bigbarbybanger (pronounced, big-barby-banger) fighterbay could be trhe fighter carrier. but if you invest everything into one big warship like the collosuss, the shivans will go
MMMMMmmmm. TSOUP