Remington is the best made between the two companies, and between those two models, the 700 is a better machine, IMHO--I've sold about 50 700s at my job, and maybe (?) 1 semi. The 700 is just so inherently versatile, and you can do just about anything to them; keep it stock, free float it & glass bed, etc. Plus, you can use a wider variety of loads than in a semi.
And the 7400 is just kinda weird; shoulders strange, feels like a shotgun.
As far as accessories, the 700 probably has more toys out there; an incredible number of people use them, and the market supports them well.