I'm pro-Giggs.
I understand that it's a gamble, and I acknowledge that a big part of the reason I want him as our next manager is the sentiment and romance of it all. I'm sure that's the same for many on the pro-Giggs side of things.
That said, he has the coaching badges, he knows the club, he knows the players, and he knows what is expected of him and everyone he will be in charge of.
The main argument against Giggs is that he won't have any managerial experience if he is given the job when van Gaal goes. There's no arguing against that because it's true. However, hiring anyone to be Manchester United manager is a gamble when the expectations are so high.
The list of (potentially) eligible successors to van Gaal includes Guardiola, Ancelotti and Mourinho, amongst other slightly less fancied names. It's very easy to create arguments against hiring any of them, particularly when you're framing their hypothetical appointments as gambles.
Guardiola has never managed in the Premier League and only has experience of taking over already brilliant sides in somewhat uncompetitive leagues. It would be a gamble to hire him when he's unproven at managing an underdog in a very competitive league.
Ancelotti hasn't been at a club that doesn't burn through money and players like there's no tomorrow since he left AC Milan in 2009. It would be a gamble to hire a manager who hasn't managed a club without a policy for annually high expenditure and player turnover when we like to develop young players.
Mourinho has strong connections to a direct rival and has a track record for burning out teams within just a few seasons. It would be a gamble to hire a manager whose sole focus is on the short-term when we're a club with a history of building for the long-term.
Giggs is going to be a gamble whatever he achieves before (hypothetically) being given the United job. Personally, I'd like to see us take that gamble sooner rather than later. This doesn't mean I want Manchester United to lower their standards, it just means I'd love to see us win things with one of our own leading the way.