I have an decent amount of legendaries but i don't know which ones to use for my attack and defense teams. Can anyone help? My legendaries are listed below.

General Nishant: Lvl 85
Arch Knight: Lvl 60
Rockantuim: Lvl 25
Goldfield: Lvl 61
Nemestrinus: Lvl 85
Vadamagma: Lvl 25
Trilops: Lvl 85
Glitch: Lvl 52
Arcade: Lvl 28
Sir Slumberly: Lvl 70
Plymouth: Lvl 85
Caillech: Lvl 60
Saika: Lvl 24
Kassia: Lvl 70
Terrorizer: Lvl 43
Son Cookie: Lvl 85
General Holter: Lvl 80
Darkzgul: Lvl 41
Lau Lau: Lvl 25
Rocigon: Lvl 54
Makugan: Lvl 100
Thorder: Lvl 100
VoltaiK: Lvl 100
Ouros: Lvl 100
Lord Moltus: Lvl 90

Most of them can go higher than they are and i can always level them up, thanks!

I forgot Ursus but hes not hatched yet

I know this probably isn't what you want to hear, but I wouldn't worry too much about being very competitive just yet. The first thing you need to do is get all those legendaries up to at least level 50. That will maximize their gold production, allowing you to grow more food, allowing you to level them all up even further. If you don't have your boosts built, build all of them to help with the gold production. If you don't have your temples and farms upgraded all the way, do that (and then grow as much food as your gold income will allow). Once that all happens and it's easy to immediately get a monster to level 100, then you'll be in a good spot to start being competitive.

For your attack team, one of your best deniers, in my opinion, is going to be Saika. Rocigon is a good supporter and you've got a few attackers to choose from in General Nishant, Makugan, and VoltaiK (don't use VoltaiK if your enemy has a monster with anticipation though, although I'm guessing that's less of an issue in whatever league you're currently in).

I actually don't use a strong defense team. Instead, I use a single common monster. This way I can get a lot of relatively easy revenge attacks. I only change up my defense team the last day of the PvP season. Keeps me in my league quite easily.