Getta Robo/Getta Robo G-It seems to less useful as a damage dealer than it used to be. But the good thing is that it's dodging ability's been boosted up quite a bit (esp in conjunction with the Mach Special and Open Gett). Upgrading this unit gets expensive and fast.
Great Mazinger-This was my overall favorite unit for Part 1, which was a surprise to me since I didn't like the Mazinger units much in the previous games (yes, all 11 in games I've played). It's powerful, it's upgrades are affordable, and it has Great Booster (4900 damage max range 2-9), and since it has support attack, it makes the perfect 2nd unit for a boss killer. As the main boss killer unit I used Daitarn 3 when I had him, and then switched over to Dangaioh
Shining Gundam-Eh, not bad...could be better.
God Gundam-Now THIS is what I'm talking about. You need to upgrade EN like crazy on this one though.
Nobel Gundam-One of the best support units in the game. It's attacks are comparable to shining Gundam, and it has support skills. Whee!
Alt-Eisen-This unit either kicks ass or blows depending on how much you upgrade it. It becomes a killer once you give it lots of HP and armor and upgrade its weapons. That and it counters automatically once it's morale is above 120. Probably the best support unit in the game (well..part 1)
Ez-8-The second best support unit. It starts off weak but it's upgrades are really cheap, so you can have all weapons dealing 2500 plus quite quickly. Too bad it's best attack is one shot....
Dangaioh-I like it. A lot. Psyhic Cut does a lot of damage and Mia heals 20% of her SP her turn, so you can essentially get away with doing "flash" every single turn.
Billbine-The Dunbine cast in general's pretty useful, mainly due to the fairies you get. Billbine makes the perfect enemy "weakener" and kicks a lot of ass if you're prepared to upgrade him enough for his weapons to do enough damage.
Todd's Dunbine-Just wanted to note that the weapons on this one is a bit more powerful than Shou's(Marvel's). I like the dark color better, to boot.
G3-Gundam-Pretty darn good. It's upgrades are cheap, so it's easy to make it a viable fighting unit. Same thing for Char's Zaku.
Bernie-You can abuse his self-destruct ability by putting him on a unit like the Re-Gz and having him use it twice :)
Also, the spell that heals 10SP to a single unit will heal 10SP to all pilots inside it, including the caster if it's the same unit. So it's more useful than it first seems...esp if a pilot with SP heal has it (like Mia)