Wilshire was excellent last year, but played as a defensive midfielder, he's shown what he can do offensively for Bolton, for England and the odd rare game for Arsenal. In terms of form and multiple great seasons he's not there yet. I'd be grateful at this point to see him have another 2/3 long season without getting injured.
As for best midfielder, anyone that doesn't say Lampard is out of his mind. Even at Scholes best, Lampard has been excellent defensively and scored and assisted more.
There has never, and likely will never be a midfielder who has shown Lampards consistency or outright contribution in goals and assists.
He had his first injury hit season last year, came back into a struggling Chelsea team, and was dropped several times and played under a manager that was doing just about everything possible to hurt his confidence and form, and he still scored 21 goals in the league alone in the past 2 shorter than normal(for him) seasons.
Before that 22 goals and 14 assists, 34 goals and 17 assists for club and country. That is outstanding. He had a "poor" season this year and got 19 goals and 10 assists for club and country, Yaya got 9 goals, 9 assists, with vastly more in form strikers ahead of him.
Lampard has not scored less than 10 in the league for 9 years, that is simply incredible, barely any strikers can make a claim like that(in any league/if they've moved to other teams or not). He's got 10 or more assists in 7 of those seasons(one of those being his only injury hit season, in all competitions). Gerrard, often talked about as better, has only scored over 10 three times in the past decade and not gotten above 10 assists 5 times.
Gerrard isn't a bad player, he was exceptional until a few years ago, yet Lampard has consistently outscored and out assisted one of the best in the league.
Yaya is great, but he spends long spells in multiple games barely running, though he still manages to burst around now and then, his fitness is definitely an issue. Also Yaya went 2-3 months playing barely average during City's spell of dropping points which almost cost them the league.
I love Scholes but ultimately he hasn't had a good scoring season in almost 7 years, before they he was a 8-14 goal a season player, below what Lampard has averaged the past decade but still very good. Since then its lucky to get above 4 goals a season and hasn't scored more than 7 in all competitions since the 04/05 season. Stunningly good passer, rash defensively(but not incapable, he just likes showing the other team he's there), but ultimately Lampard is better defensively and contributes more direct game winning goals/performances.