I'm pretty certain Eva's are even bigger than Gundams and I definitely don't see the first Gundam taking a win over Eva-01 xD. The super saiyan versions in G-Gundam though...different story in my opinion.
Man I'd love if there was a crossover and Ritsuko Akagi was just like "AN ANGEL IS ATTACKING, WAIT...IT'S FIGHTING SOMETHING....SOMEONE?!? BU..BUT HOW?!" and you just hear "HAHAHAHAHA! I'M THE UNDEFEATED OF THE EAST!!!" and it's just Master Asia xD.
Beam rifles are really nasty. The Eva's magic (AT field), but they don't always have that up and just a few shots could do it in sans AT field. So, the question is really 'can the Gundam catch it with the AT field down before running out of ammo?'. Considering the Evas practiced more with neutralizing AT fields than projecting it, the Gundam's in good shape.
Though the size of Eva weapons would make them quite dangerous... I don't really see one of the top aces being hit by the rifle (small, agile target), but if they were it'd do a lot of damage.
The best answer for the Eva is probably charge into HtH and tackle the Gundam!
Eva punts the Gundam. Those things are fast and *way* bigger. Even the beam saber won't go near deep enough.