Walter vs. Anderson

Scenario 1: Old Walter vs. Normal Anderson

Scenario 2: Vampire Walter vs. Normal Anderson

Scenario 3: Vampire Walter vs. Nail Anderson

Hm, I'd say Anderson solidly, Walter solidly, and... I think Nail Anderson, though Vamp Walter was able to dish out damage more than practically anyone else in the manga so he does have a chance.

1. Anderson
2. Prolly Walter
3. Nail Anderson wrecks

Walter loses in the first scenario, but he'll put up a fight. in the second scenario, he wins since he's pretty much merciless and is far faster and stronger, not to mention his skill with his wire is restored in that state. as for the last one though, it's hard to tell since both are very tough. if Anderson can get him with his bayonets in that state though, Walter might not be able to take it since his regeneration isn't anywhere near Alucard's level.

It should be noted that Nail Anderson is arguably the fastest character in Hellsing.

Dood impaled Alucard with his bayonets before he could even react.

true, but I think Walter could at least last for a bit given how he was trouncing Alucard in volume 9 before he started to feel the effects of his rash surgery.