The following light bulbs are physically interchangeable for the MGA tail light and brake light function (and turn signals on the MGA 1500 model). The first five are common incandescent bulbs. The H1157 is a dual filament halogen bulb.

Model  Filament   Volts      Watts       Amps        CP    Life
2057   Low-High  14.0-12.8  6.86-26.88  0.49-2.10   2-32  5000-1200
1034   Low-High  14.0-12.8  8.26-23.04  0.59-1.80   3-32  5000- 200
1157   Low-High  14.0-12.8  8.26-26.88  0.59-2.10   3-32  5000-1200
2397   Low-High  14.0-12.8  6.72-28.54  0.48-2.23   2-40  5000- 400
2357   Low-High  14.0-12.8  8.26-28.54  0.59-2.23   3-40  5000- 400
H1157  Low-High  14.0-12.8  15-50       1.07-3.90  25-107  400- 400

2057   Dim tail light, high contrast
1034   Efficient, but short life
1157   Common type dual filament bulb
2397   Dimmer/brighter and higher contrast
2357   Brighter brake light (my preferred tail light for the MGA)
H1157  Very bright, but with problems.

HALOGEN bulbs: The H1157 halogen bulb is indeed very bright, but also overkill with the following problems.

a.) The running tail light low filament is nearly as bright as a normal brake light. This is easily seen in daylight conditions, but may be mistaken for a constantly on (stuck) brake light.

b.) The high filament brake light is also very bright, but may not appear to have sufficient contrast to the abnormally bright low intensity tail light. So a driver in a following car may not so quickly notice the brake light come on over the brightness of the tail light. This is the bit that bothers me the most, both as the driver and as the follower.

c.) A not often mentioned characteristic of halogen lamps is a slow warm up, meaning there is a very small delay while the light comes up gradually, not instant on. This may further aggravate the previous problem.

d.) The 50 watt high filament generates effectively 50 watts of heat, which is sufficient to melt the MGA tail light lens if it is on for extended periods of time, like sitting in stuck traffic with your foot on the brake. In fact the 15 watt low filament may be sufficient to cause some discoloration and hazing of the lens after extended usage. In case the tail light and brake light are on at the same time you have 65 watts of heat. The light output itself does not account for very much power, as may be seen with the very efficient and cool running LED lamps.

e.) The glass of a halogen bulb must be kept meticulously clean and dry at all times, as it runs at exceedingly high temperature. Do not touch the glass of a hot one for obvious reasons. Touching the glass of a cold one will leave oils from your fingers on the glass and cause uneven heating which may explode the bulb. A good regimen is to clean the glass with rubbing alcohol and not touch it afterward.