Decent WHEEELS will be your biggest concern.
For you, I'd search Craigs list etc. for a Specialized Hard Rock, Rock Hopper or similar for a starter bike. They have a STOUT frame.
Get the wheels professionally trued/tensioned. (important)
Ride it for awhile and then decide what you want in a new bike. IF you like the bike you bought, invest in a new, STRONGER wheel set if needed.
Without "some" recent biking experience, your first choice often doesn't seem quite as good a couple months down the road.
$3-400 bikes don't tend to have the quality of wheels you need.