Well, it depends. Can you afford two? Or only one?
If one: Samurai Saramanda E230 ES. Saramada is good for defense, and when you have enough money for two, you can Synchrom it. E230 is an amazing track for defense. Samurai and ES have no real use, but the other two parts make up for it.
If two: Buy the on I stated above and Guardian Revizer. I say this because You can Synchrom Saramanda and Revizer to make Saramanda Revizer. It is good for defense. Add E230 and some extra MSFs and stick a CS on the bottom, and you have a great custom already.
Hope this helps.
@ EarthSerpent101: Flame Byxis and Big bang Pegasus are not Zero-G beys, and they are outclassed. Please do not post responses to questions you do not know the answer to.
4/29/12: The Spring Sortie (BB-10)
7/22/12: The Triple Threat (MFB+Plastics+HMS formats)
9/23/12: Autumn's Assault (Zero G)
October 2012: October Achtung (Zero G) (placed second)
12/15/12: Holiday Havoc! (Zero-G)
2/24/13: Paper vs. Plastic (Zero-G+Plastic Formats)
4/21/13: BR Maryland Qualifier (Zero-G)
5/26/12: BeyDays 2013! (BB-10) (placed first)
7/14/13: Heated Metal Plastic-y Madness! (HMS + Plastics) (placed third in HMS)
7/20/13: The Bey Brawl! (BB-10)
9/28/13 "OK, alright, mirai~!" (BB-10) (placed second)
12/15/13 No Limit Holdem'! (Zero-G, Limited)
1/19/14 Happy Gnu Year! (Zero-G)
2/23/14 Better Late Than Never! (Limited, Plastics, which I got 3rd in)
3/29/14 GBT2 North Carolina Qualfier (Limited, got 4th)
3/30/14 GBT2 Maryland Qualifier (Limited)
6/8/14 A Prehistoric Venture (Limited, HMS, placed first in HMS)
6/21/14 A Timely Farewell (Standard, Tag-Team (not official format), Zero-G, placed first in tag-team and third in Zero-G)