Two very different WRs to compare.
Allen is all quick-twitch physicality. He plays a very muscular game and will put his body on the line. He fights for every yard. Does have speed and a good change of direction, but not what you'd call a smooth runner. He looks very suited to the WCO to me. After his decommitment from Alabama to play with his brother and then the way he reacts to his brother's pretty wild QB play, I'm a little worried about him being a diva receiva. No other basis for the impression than that, but it's a gut feeling. He's made for the NFL though. Whoever drafts him won't discover he wasn't physically up to it, that's for sure. The character side is another question though, for me.
Patterson is just ridiculously smooth. He has amazing burst from the off and plenty of long speed. But it's the way he changes direction with the maximum efficiency and minimum loss of speed that makes him such a threat. Vision is superb and not prone to cutting laterally to find space. Has a great head fake and double move. Big guy - a very tough matchup for a DB but probably doesn't play to his size like Allen does.
He looks very raw to me though and I don't know if he'll be a WCO WR at the end of it. If we had the time and the coach to develop him, I'd prefer him over just about anyone. But I don't believe Ireland will take the gamble of picking a player in a massive need position who isn't ready for the NFL in Year 1. Certainly, his draft history suggests he won't.